Algorithms for use of load information from neighboring nodes in adaptive routing

ABSTRACT

Systems and methods are provided for passing data amongst a plurality of switches having a plurality of links attached between the plurality of switches. At a switch, a plurality of load signals are received from a plurality of neighboring switches. Each of the plurality of load signals are made up of a set of values indicative of a load at each of the plurality of neighboring switches providing the load signal. Each value within the set of values provides an indication for each link of the plurality of links attached thereto as to whether the link is busy or quiet. Based upon the plurality of load signals, an output link for routing a received packet is selected, and the received packet is routed via the selected output link.

RELATED APPLICATIONS

This application is a continuation of and claims the priority of U.S.patent application Ser. No. 17/594,736, filed Oct. 28, 2021, which is a371 National Stage Entry of PCT/US2020/024129, filed on Mar. 23, 2020,which claims the benefit of U.S. Provisional Patent Application No.62/852,273, filed May 23, 2019, U.S. Provisional Patent Application No.62/852,203, filed May 23, 2019, and U.S. Provisional Patent ApplicationNo. 62/852,289, filed May 23, 2019, the disclosures of which areincorporated herein by reference in their entirety for all purposes.

STATEMENT OF GOVERNMENT RIGHTS

The invention(s) described herein were made with U.S. Government supportunder one or more of the contracts set forth below. The U.S. Governmenthas certain rights in these inventions.

Contract Title Customer/Agency Contract Reference FastForward-2 LawrenceLivermore National Subcontract B609229 under prime Security, LLC/Dept ofEnergy contract DE-AC52-07NA27344 BeePresent Maryland Procurement OfficeH98230-15-D-0020; Delivery Order 003 SeaBiscuit Maryland ProcurementOffice II98230-14-C-0758 PathForward Lawrence Livermore NationalSubcontract B620872 under prime Security, LLC/Dept of Energy contractDE-AC52-07NA27344 DesignForward The Regents of the University ofSubcontract 7078453 under prime California/Dept of Energy contractDE-AC02-05CII11231 DesignForward-2 The Regents of the University ofSubcontract 7216357 under prime California/Dept of Energy contractDE-AC02-05CII11231

DESCRIPTION OF RELATED ART

As network-enabled devices and applications become progressively moreubiquitous, various types of traffic as well as the ever-increasingnetwork load continue to demand more performance from the underlyingnetwork architecture. For example, applications such as high-performancecomputing (HPC), media streaming, and Internet of Things (IOT) cangenerate different types of traffic with distinctive characteristics. Asa result, in addition to conventional network performance metrics suchas bandwidth and delay, network architects continue to face challengessuch as scalability, versatility, and efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure, in accordance with one or more variousembodiments, is described in detail with reference to the followingfigures. The figures are provided for purposes of illustration only andmerely depict typical or example embodiments.

FIG. 1 illustrates an example network in which various embodiments maybe implemented.

FIG. 2 illustrates an example switching system that facilitates flowchannels in accordance with various embodiments.

FIG. 3A illustrates crossbars implemented within an example crossbarswitch in accordance with various embodiments.

FIG. 3B illustrates an example tile matrix corresponding to ports of theexample edge switching system of FIG. 2 in accordance with variousembodiments.

FIG. 3C illustrates an example tile making up the tile matrix of FIG. 3Bin accordance with various embodiments.

FIG. 3D illustrates an example age queue implementation in accordancewith various embodiments.

FIG. 4A and FIG. 4B are block diagrams of an example FRF componentimplemented at each port of the example edge switching system of FIG. 2.

FIG. 5 illustrates an example of route selection in accordance withvarious embodiments.

FIG. 6 illustrates an example of local and global load value updatingand use in accordance with various embodiments.

FIG. 7A illustrates an example of average load-based routing.

FIG. 7B illustrates an example of neighboring switch load-based adaptiverouting in accordance with various embodiments.

FIG. 8 illustrates an example computing component capable of executinginstructions for load-based adaptive routing in accordance with oneembodiment.

FIG. 9 is an example computing component in which various embodimentsdescribed herein may be implemented.

The figures are not exhaustive and do not limit the present disclosureto the precise form disclosed.

DETAILED DESCRIPTION

The present disclosure describes systems and methods that canaccommodate exascale computing, e.g., perform data-intensive tasks suchas simulations, data analytics, artificial intelligence workloads atexascale speeds. In particular, an HPC network or interconnect fabric isprovided that may be Ethernet-compatible, able to connect to third-partydata storage, and can be built using a switch component that isextremely high bandwidth, e.g., on the order to 12.8 Tb/s/dir per switchwith, e.g., 64 200 Gbps ports that support large network creation withvery low diameter (e.g., only three network hops). Moreover, low latencycan be achieved through novel congestion control mechanisms, adaptiverouting, and the use of traffic classes that allows for flexibility interms of bandwidth shaping, priority, and routing policy.

When passing information from switch to switch, it is necessary to makeinstantaneous decisions about the next hop on the path. Decisions aretaken using information derived from local state and information that iscommunicated from neighboring switches. Use of information from manydifferent sources allows for more accurate/effective decisions. Thisincludes information from neighbors.

Prior systems carried information on average load from switch to switch.That said, more detailed information from related or neighboringswitches is more helpful. Accordingly, in some embodiments, a set ofvalues can include information indicative of the status of output portsof related/neighboring switches. By passing this set of values, muchbetter routing decisions can be made. In one example, a flag is passedback from neighboring switches, with the flag having one bit for eachoutput port. For example, with a switch having 64 outputs, a 64 bit flagwould be transmitted. This is much more accurate than simply passing aglobal average for neighboring ports.

FIG. 1 shows an example network 100 comprising a plurality of switches,which can also be referred to as a “switch fabric.” As illustrated inFIG. 1 , network 100 can include switches 102, 104, 106, 108, and 110.Each switch can have a unique address or ID within switch fabric 100.Various types of devices and networks can be coupled to a switch fabric.For example, a storage array 112 can be coupled to switch fabric 100 viaswitch 110; an InfiniBand (IB) based HPC network 114 can be coupled toswitch fabric 100 via switch 108; a number of end hosts, such as host116, can be coupled to switch fabric 100 via switch 104; and anIP/Ethernet network 118 can be coupled to switch fabric 100 via switch102. For example, a switch, such as switch 102 may receive 802.3 frames(including the encapsulated IP payload) by way of Ethernet devices, suchas network interface cards (NICs), switches, routers, or gateways. IPv4or IPv6 packets, frames formatted specifically for network 100, etc. mayalso be received, transported through the switch fabric 100, to anotherswitch, e.g., switch 110. Thus, network 100 is capable of handlingmultiple types of traffic simultaneously. In general, a switch can haveedge ports and fabric ports. An edge port can couple to a device that isexternal to the fabric. A fabric port can couple to another switchwithin the fabric via a fabric link.

Typically, traffic can be injected into switch fabric 100 via an ingressport of an edge switch, and leave switch fabric 100 via an egress portof another (or the same) edge switch. An ingress edge switch can groupinjected data packets into flows, which can be identified by flow ID's.The concept of a flow is not limited to a particular protocol or layer(such as layer-2 or layer-3 in the Open System Interface (OSI) referencemodel). For example, a flow can be mapped to traffic with a particularsource Ethernet address, traffic between a source IP address anddestination IP address, traffic corresponding to a TCP or UDP port/IP5-tuple (source and destination IP addresses, source and destination TCPor UDP port numbers, and IP protocol number), or traffic produced by aprocess or thread running on an end host. In other words, a flow can beconfigured to map to data between any physical or logic entities. Theconfiguration of this mapping can be done remotely or locally at theingress edge switch.

Upon receiving injected data packets, the ingress edge switch can assigna flow ID to the flow. This flow ID can be included in a special header,which the ingress edge switch can use to encapsulate the injectedpackets. Furthermore, the ingress edge switch can also inspect theoriginal header fields of an injected packet to determine theappropriate egress edge switch's address, and include this address as adestination address in the encapsulation header. Note that the flow IDcan be a locally significant value specific to a link, and this valuecan be unique only to a particular input port on a switch. When thepacket is forwarded to the next-hop switch, the packet enters anotherlink, and the flow-ID can be updated accordingly. As the packets of aflow traverses multiple links and switches, the flow IDs correspondingto this flow can form a unique chain. That is, at every switch, before apacket leaves the switch, the packet's flow ID can be updated to a flowID used by the outgoing link. This up-stream-to-down-stream one-to-onemapping between flow ID's can begin at the ingress edge switch and endat the egress edge switch. Because the flow ID's only need to be uniquewithin an incoming link, a switch can accommodate a large number offlows. For example, if a flow ID is 11 bits long, an input port cansupport up to 2048 flows. Furthermore, the match pattern (one or moreheader fields of a packet) used to map to a flow can include a greaternumber of bits. For instance, a 32-bit long match pattern, which caninclude multiple fields in a packet header, can map up 2{circumflex over( )}32 different header field patterns. If a fabric has N ingress edgeports, a total number of N*2{circumflex over ( )}32 identifiable flowscan be supported.

A switch can assign every flow a separate, dedicated input queue. Thisconfiguration allows the switch to monitor and manage the level ofcongestion of individual flows, and prevent head-of-queue blocking whichcould occur if shared buffer were used for multiple flows. When a packetis delivered to the destination egress switch, the egress switch cangenerate and send back an acknowledgement (ACK) in the upstreamdirection along the same data path to the ingress edge switch. As thisACK packet traverses the same data path, the switches along the path canobtain the state information associated with the delivery of thecorresponding flow by monitoring the amount of outstanding,unacknowledged data. This state information can then be used to performflow-specific traffic management to ensure the health of the entirenetwork and fair treatment of the flows. As explained in more detailbelow, this per-flow queuing, combined with flow-specific deliveryacknowledgements, can allow the switch fabric to implement effective,fast, and accurate congestion control. In turn, the switch fabric candeliver traffic with significantly improved network utilization withoutsuffering from congestion.

Flows can be set up and released dynamically, or “on the fly,” based ondemand. Specifically, a flow can be set up (e.g., the flow-ID to packetheader mapping is established) by an ingress edge switch when a datapacket arrives at the switch and no flow ID has been previously assignedto this packet. As this packet travels through the network, flow IDs canbe assigned along every switch the packet traverses, and a chain of flowIDs can be established from ingress to egress. Subsequent packetsbelonging to the same flow can use the same flow IDs along the datapath. When packets are delivered to the destination egress switch andACK packets are received by the switches along the data path, eachswitch can update its state information with respect to the amount ofoutstanding, unacknowledged data for this flow. When a switch's inputqueue for this flow is empty and there is no more unacknowledged data,the switch can release the flow ID (i.e., release this flow channel) andre-use the flow-ID for other flows. This data-driven dynamic flow setupand teardown mechanism can obviate the need for centralized flowmanagement, and allows the network to respond quickly to traffic patternchanges.

Note that the network architecture described herein is different fromsoftware-defined networks (SDN's), which typically uses the OpenFlowprotocol. In SDN, switches are configured by a central networkcontroller, and packets are forwarded based one or more fields in thelayer-2 (data link layer, such as Ethernet), layer-3 (network layer,such as IP), or layer-4 (transport layer, such as TCP or UDP) headers.In SDN such header-field lookup is performed at every switch in thenetwork, and there is no fast flow ID-based forwarding as is done in thenetworks described herein. Furthermore, because the OpenFlowheader-field lookup is done using ternary content-addressable memory(TCAM), the cost of such lookups can be high. Also, because theheader-field mapping configuration is done by the central controller,the setup and tear-down of each mapping relationship is relatively slowand could require a fair amount of control traffic. As a result, an SDNnetwork's response to various network situations, such as congestion,can be slow. In contrast, in the network described herein, the flows canbe set up and torn down dynamically based on traffic demand; and packetscan be forwarded by a fixed-length flow ID. In other words, flowchannels can be data driven and managed (i.e., set up, monitored, andtorn down) in a distributed manner, without the intervention of acentral controller. Furthermore, the flow ID-based forwarding can reducethe amount of TCAM space used and as a result a much greater number offlows can be accommodated.

Referring to the example shown in FIG. 1 , suppose that storage array112 is to send data using TCP/IP to host 116. During operation, storagearray 112 can send the first packet with host 116's IP address as thedestination address and a predetermined TCP port specified in the TCPheader. When this packet reaches switch 110, the packet processor at theinput port of switch 110 can identify a TCP/IP 5-tuple of this packet.The packet processor of switch 110 can also determine that this 5-tuplecurrently is not mapped to any flow ID, and can allocate a new flow IDto this 5-tuple. Furthermore, switch 110 can determine the egressswitch, which is switch 104, for this packet based on the destination(i.e., host 116's) IP address (assuming switch 110 has knowledge thathost 116 is coupled to switch 104). Subsequently, switch 110 canencapsulate the received packet with a fabric header that indicates thenewly assigned flow ID and switch 104's fabric address. Switch 110 canthen schedule the encapsulated packet to be forwarded toward switch 104based on a fabric forwarding table, which can be computed by all theswitches in fabric 100 using a routing algorithm such as link state ordistance vector.

Note that the operations described above can be performed substantiallyat line speed with little buffering and delay when the first packet isreceived. After the first packet is processed and scheduled fortransmission, subsequent packets from the same flow can be processed byswitch 110 even faster because the same flow ID is used. In addition,the design of the flow channels can be such that the allocation,matching, and deallocation of flow channels can have substantially thesame cost. For example, a conditional allocation of a flow channel basedon a lookup match and a separate, independent deallocation of anotherflow channel can be performed concurrently in nearly every clock cycle.This means that generating and controlling the flow channels can addnearly no additional overhead to the regular forwarding of packets. Thecongestion control mechanism, on the other hand, can improve theperformance of some applications by more than three orders of magnitude.

At each switch along the data path (which includes switches 110, 106,and 104), a dedicated input buffer can be provided for this flow, andthe amount of transmitted but unacknowledged data can be tracked. Whenthe first packet reaches switch 104, switch 104 can determine that thedestination fabric address in the packet's fabric header matches its ownaddress. In response, switch 104 can decapsulate the packet from thefabric header, and forward the decapsulated packet to host 116.Furthermore, switch 104 can generate an ACK packet and send this ACKpacket back to switch 110. As this ACK packet traverses the same datapath, switches 106 and 110 can each update their own state informationfor the unacknowledged data for this flow.

In general, congestion within a network can cause the network buffers tofill. When a network buffer is full, the traffic trying to pass throughthe buffer ideally should be slowed down or stopped. Otherwise, thebuffer could overflow and packets could be dropped. In conventionalnetworks, congestion control is typically done end-to-end at the edge.The core of the network is assumed to function only as “dumb pipes,” themain purpose of which is to forward traffic. Such network design oftensuffers from slow responses to congestions, because congestioninformation often cannot be sent to the edge devices quickly, and theresulting action taken by the edge devices cannot always be effective inremoving the congestion. This slow response in turn limits theutilization of the network, because to keep the network free ofcongestion the network operator often needs to limit the total amount oftraffic injected into the network. Furthermore, end-to-end congestioncontrol usually is only effective provided that the network is notalready congested. Once the network is heavily congested, end-to-endcongestion control would not work, because the congestion notificationmessages can be congested themselves (unless a separate control-planenetwork that is different from the data-plane network is used forsending congestion control messages).

In contrast, the flow channels can prevent such congestion from growingwithin the switch fabric. The flow channel mechanism can recognize whena flow is experiencing some degree of congestion, and in response canslow down or stop new packets of the same flow from entering the fabric.In turn, these new packets can be buffered in a flow channel queue onthe edge port and are only allowed into the fabric when packets for thesame flow leave the fabric at the destination edge port. This processcan limit the total buffering requirements of this flow within thefabric to an amount that would not cause the fabric buffers to becometoo full.

With flow channels, the switches have a reasonably accurate stateinformation on the amount of outstanding in-transit data within thefabric. This state information can be aggregated for all the flows on aningress edge port. This means that the total amount of data injected byan ingress edge port can be known. Consequently, the flow channelmechanism can set a limit on the total amount of data in the fabric.When all edge ports apply this limit action, the total amount of packetdata in the entire fabric can be well controlled, which in turn canprevent the entire fabric from being saturated. The flow channels canalso slow the progress of an individual congested flow within the fabricwithout slowing down other flows. This feature can keep packets awayfrom a congestion hot spot while preventing buffers from becoming fulland ensuring free buffer space for unrelated traffic.

FIG. 2 illustrates an example switch 202 (which may be an embodiment ofany one or more of switches 102, 104, 106, 108, and 110) that may beused to create a switch fabric, e.g., switch fabric 100 of FIG. 1 . Inthis example, a switch 202 can include a number of communication ports,such as port 220. Each port can include a transmitter and a receiver.Switch 202 can also include a processor 204, a storage device 206, and aflow channel switching logic block 208. Flow channel switching module208 can be coupled to all the communication ports and can furtherinclude a crossbar switch 210, an EFCT logic block 212, an IFCT logicblock 214, and an OFCT logic block 216.

Crossbar switch 210 includes crossbars which can be configured toforward data packets and control packets (such as ACK packets) among thecommunication ports. EFCT logic block 212 can process packets receivedfrom an edge link and map the received packets to respective flows basedon one or more header fields in the packets. In addition, EFCT logicblock 212 can assemble FGFC Ethernet frames, which can be communicatedto an end host to control the amount of data injected by individualprocesses or threads. IFCT logic block 214 can include the IFCT, andperform various flow control methods in response to control packets,such as endpoint-congestion-notification ACKs and fabric-linkcredit-based flow control ACKs. OFCT logic block 216 can include amemory unit that stores the OFCT and communicate with another switch'sIFCT logic block to update a packet's flow ID when the packet isforwarded to a next-hop switch.

In one embodiment, switch 202 is an application-specific integratedcircuit (ASIC) that can provide 64 network ports that can operate ateither 100 Gbps or 200 Gbps for an aggregate throughput of 12.8 Tbps.Each network edge port may be able to support IEEE 802.3 Ethernet, andOptimized-IP based protocols as well as Portals, an enhanced frameformat that provides support for higher rates of small messages.Ethernet frames can be bridged based on their L2 address or they can berouted based on their L3 (1Pv4//1Pv6) address. Optimized-IP frames mayonly have an L3 (1Pv4/1Pv6) header, and are routed. Specialized NICsupport can be used for the Portals enhanced frame format, and can mapdirectly onto the fabric format of network 100, e.g., a fabric formatthat provides certain control and status fields to support a multi-chipfabric when switches/switch chips, such as switches 102, 104, 106, 108,and 110 are connected and communicate with each other. As alluded toabove, a congestion control mechanism based on flow channels can be usedby such switches, and can also achieve high transmission rates for smallpackets (e.g., more than 1.2 billion packets per second per port) toaccommodate the needs of HPC applications.

Switch 202 can provide system-wide Quality of Service (QoS) classes,along with the ability to control how network bandwidth is allocated todifferent classes of traffic, and to different classes of applications,where a single privileged application may access more than one class oftraffic. Where there is contention for network bandwidth, arbitersselect packets to forward based on their traffic class and the creditsavailable to that class. Network 100 can support minimum and maximumbandwidths for each traffic class. If a class does not use its minimumbandwidth, other classes may use the unused bandwidth, but no class canget more than its maximum allocated bandwidth. The ability to managebandwidth provides the opportunity to dedicate network resources, aswell as CPUs and memory bandwidth to a particular application.

In addition to support for QoS classes, switch 202 effectuates flowchannel-based congestion control, and can reduce the number of networkhops, e.g., in a network having a dragonfly topology, from five networkhops to three. The design of switch 202, described in greater detailbelow, can reduce network cost and power consumption, and may furtherfacilitate use of innovative adaptive routing algorithms that improveapplication performance. A fabric created by a plurality of switches,such as a plurality of switches 202 may also be used in constructingFat-Tree networks, for example when building a storage subsystem forintegration with third-party networks and software. Further still, theuse of switch 202 enables fine-grain adaptive routing while maintainingordered packet delivery. In some embodiments, switch 202 may beconfigured to send the header of a packet from an input port to anoutput port before the full data payload arrives, thereby allowingoutput port load metrics to reflect future loads, thereby improvingadaptive routing decisions made by switch 202.

Crossbar switch 210 may comprise separate, distributed crossbars routingdata/data elements between input and output ports. In some embodiments,and as illustrated in FIG. 3A, there are five distributed crossbarsincluding a request crossbar 210 a, a grant crossbar 210 b, creditcrossbar 210 c, an Ack crossbar 210 d, and a data crossbar 210 e betweeninput port 220 b and output port 220 c.

Request crossbar 210 a is used to send requests from an input to atargeted output age queue. Grant crossbar 210 b is used to return agrant back to the input to satisfy a request. In particular, grantcrossbar 210 b returns a pointer indicating where a packet is within aninput buffer. It should be noted that a grant is returned when there isspace in the output for the corresponding packet. Grant crossbar 201 bmay also optionally return a credit for requested space in the output.It should be noted that grants are returned when there is a landing spotfor a packet at the output, e.g., an output port 220 c, so packetscannot be blocked (though they can face transient contention forresources).

It should be understood that in accordance with various embodiments, acredit protocol may be used to guarantee that there is a landing spacefor a request at the output. Accordingly, a credit crossbar 210 c may beused to return credit for requested space in the output.

A data crossbar 210 d is used to move granted packets from an inputbuffer to a targeted output buffer. An Ack crossbar 210 e is used topropagate Ack packets from output ports 220 c to input ports 220 b. Acksare steered in accordance with a state kept in an output flow channeltable.

It should be understood that data crossbar 210 d moves multi-clockpackets with both headers and data, while the other four crossbars(request crossbar 210 a, grant crossbar 210 b, credit crossbar 210 c,and Ack crossbar 210 e) move only single-clock packet headers. All fivecrossbars use the same architecture with row buses and column buseswithin an 8×4 matrix of 32 dual-port tiles (as described below).

Referring back to FIG. 2 , switch 202 may have a plurality oftransmit/receive ports, e.g., port 220. The plurality of ports may bestructured in a tile matrix. FIG. 3B illustrates an example of such atile matrix 300. In one embodiment, tile matrix 300 comprises 32 tiles,each comprising two ports used to implement the crossbar switchingbetween ports, and to provide the following: a serializer/de-serializer(SERDES) interface between the core of switch 202 and external highspeed serial signals for driving the signals off switch 202; a mediaaccess control (MAC) sub-layer interface to the physical coding sublayer(PCS); a PCS interface between the SERDES and the Ethernet MAC function;a link level retry (LLR) function that operates on a per packet basisand uses ordered sets to deliver initialization sequences, Acks, andNacks; and and Ingress Transforms block for converting between differentframe fabric formats. Each tile contains a crossbar switch such ascrossbar switch 210 for each of the crossbars (210 a-201 e). As will bediscussed in greater detail below, routing in the switch fabric may becontrolled by a fabric routing function (FRF) implemented in switch 202,where a separate instance of the FRF component (FIGS. 4A, 4B) may beimplemented within input logic for each port of switch 202. As notedabove, each port includes an instance of the FRF component, but for easeof reference/illustration clarity, only two example FRF instances (400a, 400 b) are labeled.

Each crossbar switch 210 has sixteen inputs 220 b, one for each port inits row, and eight outputs 220 c, one for each port in its column. Rowbuses can be driven from each source in a row to all eight crossbars inthat row (one-to-all). Arbitration can be performed at the crossbar fromthe sixteen row buses in that row to the eight column buses in a givencolumn. Buffering can be provided at each 16×8 crossbar for each of therow buses in order to absorb packets during times when there iscontention for a column bus. In some embodiments, a non-jumbo packet iskept off a row bus unless there is room for the entire packet in thetargeted crossbar input buffer. Due to area constraints, jumbo packetsare allowed to go even if there is not sufficient space (crossbar inputbuffer only sized to sink a non-jumbo packet) with the row bus beingblocked until the packet wins arbitration and space is freed as it ismoved onto a column bus.

Column buses are driven from a given crossbar to each destination portwithin a column (all-to-all). Each destination may have another level ofarbitration between the column buses from the four rows. With sixteenrow buses driving eight crossbars, each feeding eight column buses,there is a 4× speedup between rows and columns. Each row has identicalconnections with the one-to-all row bus connections for a single rowshown in row buses. Each tile will have a one (request, grant, credit)or a two (data, ack) clock delay per tile depending on the crossbar.This gives a maximum seven or fourteen clock delay to get between theleftmost and rightmost columns. Credit returns routed through creditcrossbar 210 c may have a one clock delay per tile, and therefore, cantake a maximum of seven clocks to complete transmission.

It should be noted that each column may have identical connections withthe all-to-all column bus connections for a single column, and there maybe a two clock delay per tile, resulting in a six clock delay to getfrom the top row to the bottom row. It should also be understood thatboth row and column buses both use the aforementioned credit-basedprotocol to determine when they are able to send. In the case of rowbuses, the source port maintains credit counts for the input buffers ofthe crossbars within that row. For the data crossbar, care is needed todetermine when a packet is allowed to go on a row bus. If grantstargeting a particular crossbar input buffer all go through a singlequeue, space for the packet at the head of the queue is required beforestarting the packet transfer. If the grants are distributed acrossmultiple queues, in order to prevent small packets from locking outlarge packets, a packet transfer does not start unless there is spacefor an entire max sized packet in the buffer. In this way, once a packettransfer on a row bus starts, it will not stop until the entire packethas been transferred. Accordingly, crossbar input buffers are configuredto be large enough to handle the maximum packet size plus additionalspace to cover the worst case round trip (packet send to credit return).This will not be the case for jumbo packets. To save on buffering area,the crossbar input buffers are only deep enough to handle a non-jumbosized MTU (1500 bytes) with a jumbo packet being allowed to block a rowbus while waiting to gain access to the targeted column bus.

For column buses, each crossbar maintains credit counts for the inputbuffers at each destination port in that column. Unlike row buses, thereis no requirement that credits be available for a maximum-sized packetbefore starting transfer of that packet on a column bus. Individualwords of the packet will move as credits become available. Therefore,the input buffer at the destination for each column bus needs to only bebig enough to cover the worst case round trip (packet to credit).

FIG. 3C illustrates, in greater detail, an example implementation of twoports, e.g., ports 0 and 1, handled by tile 1, along with crossbar 220 acomprising a set of row buses and column channels with per tilecrossbars. In this way, every port has its own row bus, whichcommunicates across its row, and every tile has the aforementioned 16×8crossbar, which is used to do corner turns, and a set of eight columnchannels that feed up to the eight ports that are contained in thatcolumn. In other words, each crossbar switch 210 has sixteen row businput buffers and eight possible destinations. For example, for data totravel from, e.g., input port 17 to output port 52, data is routed alonga row bus from input port 17, traverses a local crossbar which is a 16to 8 arbitration, and then traverses up a column channel to output port52. In terms of the total routing through all the set of distributedcrossbars, there is four times more internal bandwidth than there isexternal bandwidth, resulting in an ability to keep up with ingress whenrouting nearly any arbitrary permutation of traffic through switch 202.

A fair round-robin arbitration may be used between the sixteen sourcesfor each destination. For the data crossbar 210 d, once a source winsarbitration, it keeps control of the destination column bus until theentire packet has been sent. Each output grants a limited amount ofpacket payload so it is expected that contention for a given column busshould be fairly limited when larger packets are involved. Because ofthis, a round-robin arbitration is expected to be sufficient even withpossibly large differences in packet size among requesters.

Parts of switch 202 associated with output functions generally operateon frames within the switch fabric format, and have a fabric header,even, for example, for a frame arriving and leaning on an Ethernet portwithin a single switch 202.

Age queue output control is responsible for accepting requests from allof the input port, e.g., input ports 220 b, via request crossbar 210 a,buffering the requests, arbitrating between them by traffic class usinga traffic shaper, and passing the requests to the OFCT 216 to be grantedvia grant crossbar 210 b. Age queue buffering is managed to allow eachinput to have enough space to flow while also allowing an input withmultiple flows targeting a given output to take more space. Inparticular, an age queue space is managed by output control. The agequeue/output control may also be responsible for managing access to thelink either using credit-based flow control for a connected input bufferor pause-based flow control for non-fabric links. When a packet isreleased by the age queue, it is committed to being put on the link.Additionally the age queue has a path allowing packets initiated on agiven port e.g., one of input ports 220 b (such as maintenance orreduction packets), to arbitrate for resources on the given port.

Requests come into the output control block via a column bus from eachrow of matrix 30. Each column bus feeds an independent FIFO (e.g.,first-in-first-out shift register or buffer) with space in the FIFOmanaged via credits. The FIFOs may be sized (24 deep) to cover around-trip plus additional space to allow requests to be moved out ofthe crossbars 210 a-210 e and prevent head-of-line blocking. Prior towriting into a FIFO, a request may be checked for a valid errorcorrecting code (ECC). If the ECC check has either a multi bit error(MBE) or a single bit error (SBE) in the destination field (i.e. it hasbeen routed to the wrong port), the request is considered to be aninvalid request, and is discarded with an error being flagged.

Least recently used (LRU) arbitration may be performed between columnbus FIFOs to choose which FIFO gets forwarded to age queue management.As requests are removed from each FIFO, credits are returned to thecorresponding crossbar. The row with which an incoming column buscorresponds can be dependent both on where in the matrix the tile islocated, and as well as which half of the tile the block is in.

The output buffer (OBUF) makes requests to the output control block forsending reduction and maintenance packets across a link. These requestsmay be given the highest priority. A FIFO with 8 locations can be usedto buffer these reduction/maintenance packet requests while they waitfor resources. Reduction packets need not use flow channels, andmaintenance packets may use loopback to create a flow so that checkingfor flow channel availability or flowing through the OFCT to create agrant is not needed. Reduction and maintenance packets also need not useany space in the output buffer so that no check of space is required.Rather, a check for the link partner input butter may be performed. Ifallowed, a shaping queue (SQ) or virtual channel (VC) can be granted,blocking any grants from the age queue path from being granted duringthat cycle.

The size of the next request to be processed from the output bugger ischecked against max_frame_size. If it exceeds this setting, the requestis not processed and an error flag is set. This will result in theoutput buffer request path being blocked until a warm reset isperformed. The error flag will stay set until the reset is done. Thecondition can also be released by increasing the setting ofmax_frame_size to a value above the size of the stuck output bufferrequest. The size used in the comparison may be the size indicated inthe output buffer request (which may include a 4-byte frame checksum(FCS) used on the wire).

Each input may be given the same fixed allocation of age queue space.This age queue space is large enough to reserve a location for eachSQ/VC with enough additional space to cover a request/credit round-trip.It is up to the input to manage the space it is given across itsSQs/VCs. This allocation (fixed_al/oc) is programmable via a control andstatus register (CSR) in each input queue (INQ), and can be, e.g., inthe range of 64-96 locations. The remaining age queue space(8K−64*fixed_al/oc) may be shared space that is available to all inputs.The shared space can be managed by the output with it moving incomingrequests from static to shared space as they arrive if there is room inthe shared space, subject to per-input limits. When moving a request tothe shared space, a credit is returned, e.g., immediately, via creditcrossbar 210 c, with the request marked in the age queue as being in theshared space.

When a request is granted, if it is marked as using the shared space,the shared space is credited. If it is not marked as using shared space,the request is considered to have used the static space, and a credit isreturned to the input with the grant.

Due to conflicts in credit crossbar 210 c, it is possible that creditsmay not be sent every clock period. Accordingly, a FIFO providesbuffering for these transient disruptions. Space in this FIFO isrequired before taking a request from the request crossbar. A FIFO witha depth of 32 locations can be used to limit the chances of it everbacking up into request crossbar 210 a. The shared space may have limitsfor how much space any input (from an input port 220 b) can take. Theselimits can be set as a percentage of the available space. For instance,if the limit is set to 50%, if one input port is active, it has accessto 50% of the buffer space, with two active input ports, each gets 37.5%((space_used_by_I+pace_left*0.5)/2=(50%+50%*0.5)/2), with three activeinput ports, each gets 29.2%((space_used_by_2+space_left*0.5)/3=(75%+25%*0.5)/3), and so on.Additionally, the total space used by the active input ports can belimited to the given total (50%, 75%, 87.5%). Thus, the space allocatedto each of input port 220 b may vary dynamically by how many inputsports are currently active. The addition of an active input port causesother active inputs ports to give up their space which is then taken bythe new input.

Given that division is not something easily done in hardware, theaforementioned age queue credit management function can be implementedas a lookup table 310 with 64 entries 312. The number of inputscurrently active in the age queues 320 indexes 315 the lookup table 310.The values 314 in the lookup table 310 reflect the limit of the numberof shared space locations any input can take along with the total spacethey can consume as a whole. Thus, it is up to software to program thevalues 314 in the lookup table 310 according to how much total sharedspace there is and what percentage each input port is allowed to take.As more input ports 220 b become active, each input port 220 b isallowed less space, and the total space available increases. Incomingrequests from input ports 220 b that are above this limit, or in total,exceed the total space limit, are not allowed to take more shared space.In order to track the number of active input ports 220 b in the agequeues, a set of 64 counters 316 (one for each input port) is used.These count up when a request is put in the age queues 320 and countdown as they are taken out (i.e., granted). A count of the number ofnon-zero counts 319 is used as an index into the lookup table 310. Inaddition, in order to manage the shared space, an additional set of 64counters 318 may be used to track the current usage of the shared spaceby each input. There may also be a single counter 334 that can be usedto track overall shared space usage. These counters are compared againstthe current quotas to determine if a request is allowed to use theshared space or not. Counters 316, 318 can be, e.g., 13 bits wide, toprovide sufficient coverage of the maximum value of an object that maybe somewhat less than 8K.

Age queues 320 may use a single storage RAM 321 that has 8K locations init. These locations can be dynamically allocated to 32 separate queues(one for each SQ/VC) with each consisting of a linked-list of locationswithin the storage RAM 321. This gives each SQ/VC the ability to takemore space as needed.

An age queue 320 can be created with a front pointer 322 pointing to thefront of the queue, and a next pointer 324 for each location pointingthe next item in the queue. The last location in the queue may beindicated by a back pointer 326. Items are taken from the front of thequeue and inserted at the back of the queue. In addition to the abovedata structures, each queue has a FIFO 328 of entries at its head. TheseFIFOs 328 may ensure that a queue can sustain a request every clock witha multi-clock read access time from the request RAM 321. When a newrequest arrives, if the head FIFO 328 328 for that queue is not full, itbypasses the request RAM 321, and can be written directly into the headFIFO 328. Once requests for a given age queue are being written to therequest RAM 321, subsequent requests are also written to the request RAM321 to maintain order. The bypass path can be used again once there areno more requests for that age queue in the request RAM 321, and there isroom are the head FIFO 328. When a request is read from a head FIFO 328,and there are corresponding requests queued in the request RAM 321, adequeue is initiated. One head FIFO 328 may be read at a time, such thata single dequeue operation can be initiated each clock period. Logic maybe included to handle the various race conditions between an ongoing orimminent enqueue operation and a head FIFO 328 being read.

The aforementioned ECC protection used in the age queue RAM 321 can beextended to the FIFOs 328 to protect the data path flops. The resultingstructure may include 8K flops (32 queues×5 deep×SQ-bits wide). Whengenerating the ECC, the age queue number can be included in thecalculation (but not stored) as an extra check of the free listmanagement. When the ECC is checked, the request can be considered to bein error if there is an MBE or there is an SBE in the queue number bits.

A free list RAM can be a simple FIFO which is initialized with pointersto all 8K entries whenever a reset is performed. A count can bemaintained to keep track of how may entries are valid within the freelist. As entries are taken, they are popped off the front of the FIFOand used. As entries are returned, they are pushed onto the back of theFIFO. Some number of entries, e.g., three entries,) at the head of thefree list can be kept in flops so they are available for quick access.As with the head FIFOs for the age queues, ECC is carried through theflops to provide protection. The resulting structure may have minimalflops (57=3 deep×19-bits wide).

In order to support full performance for small packets, age queuessupport both an enqueue and a dequeue every clock period. The operationsacross the data structures for an enqueue operation are discussed below,and can differ depending on whether the queue being written is empty ornot.

In some cases, a simultaneous enqueue and dequeue to a specific queue iseasily handled as they are using and updating separate fields. Somespecialized scenarios may arise, e.g., when a dequeue operation emptiesthe age queue. In order to handle this scenario, a dequeue occurs firstlogically, followed by an enqueue operation. Accordingly, an empty flagis seen as being set when the queue is emptied by the dequeue operation,and then cleared due to the enqueue operation.

The arbitration alluded to above can be performed among requests thatare permitted to be granted subject to input buffer management, outputbuffer management, and flow channel quotas. Arbitration can also behalted if there are no credits for the OFCT input FIFO. In someembodiments, arbitration may be performed at two levels. First, trafficshaping arbitration can be used to arbitrate between the SQs. A DeficitRound-robin arbitration can be used to arbitrate between VCs within agiven SQ. Traffic shaping arbitration may use a series of token bucketsto control the bandwidth of each SQ as follows: eight leaf buckets, onefor each SQ; four branch buckets; and a single head bucket.

Arbitration can be divided into three groups with a first group havingthe highest priority, followed by a second group, which in turn isfollowed by a third group. For the first and second groups, arbitrationmay be handled in the same way among eligible SQs. A ×8 round-robinarbitration can be performed between the SQs for each of the eightpriority levels (eight parallel round-robin arbitrations). A fixedarbitration can be performed between priority levels. For example, group3 arbitration has no priorities, and therefore is simply a single ×8round-robin arbitration.

For arbitration in the first group, the priority for each comes from thesetting in the leaf buckets. For arbitration in the second group,priority comes from the setting in the branches of the leaf buckets. Inall cases, the buckets which are checked to be eligible for that group,are also the buckets from which packet size tokens are obtained if thatrequest wins arbitration.

Regarding age queue 320 selection, packets can be classified in order toselect the SQ to which their request is forwarded. This allows trafficassociated with an application to be shaped differently from trafficoriginating from a different application or a different traffic class.This can be useful on the edge ports which connect to a NIC in that theapplications will have been configured to use a share of the resourceson the node, and similarly will be granted a proportion of the networkbandwidth. In accordance with one embodiment, this classification isperformed by classifying the packets into a traffic class identifier(FTAG), e.g., a 4-bit code that is part of the fabric frame header, anda VLAN ID (VNI) as the packet ingresses into the fabric. The FTAG andVNI may then be used as the packet egresses the fabric to select theshaping queue.

A configuration register can be used to map FTAGs to SQs. Thisconfiguration matches the corresponding configuration in the in queue.When the output buffer requests or returns link partner credits, itconverts a given FTAG to an SQ. For packet injection, the FTAG is foundin R_TF_OBUF_CFG_PFG_TX_CTRL. For test generation, the FTAG is found inthe test control register. When the reduction engine (RED) requests acredit return, the FTAG is found in ret_cdt/tag. When a reduction frameis removed from the output stream and link partner credits need to bereturned, the FTAG is found in the frame header.

Regarding the SQs discussed herein, each age queue 320 may have 32 SQsthat are addressed by {SQ, VC}. The 3-bit SQ 330 can be considered ashaping function, and the VC selects one of four queues within thatshaping function. For Ethernet egress (edge) ports, the VC is not neededfor deadlock avoidance. Accordingly, all 32 SQs 330 can be available. Insuch a scenario, the SQ 330 can be selected by adding the SQ base fromR_TF_OBUF_CFG_FTAG_SQ_MAP to the lower bits of the VNI. The 5-bit sumdefines the {SQ,VC} to send to the age queue. It should be noted thatwhen injecting frames on an egress port, a VNI is not available, andtherefore, an SQ base can be directly used. For fabric links, the SQ 330is taken from the upper three bits of the SQ base. The VC can be takenfrom the frame header when returning credits for reduction frames, orfrom the appropriate control CSR (R_TF_OBUF_CFG_TEST_CTRL orR_TF_OBUF_CFG_PFG_TX_CTRL) when injecting frames.

A link partner input buffer management can depend on the type of deviceto which the link is attached. Devices such as switch 202 may usecredit-based flow control where each credit represents a cell of storagein the input buffer. Other devices may use standard Ethernet pause orpriority pause-based flow control. Requests which are marked toterminate locally (lac term set) need not consider link partner inputbuffer flow control and need not update any associated counters. Linkpartner space need not be considered when the link is in the drainingstate.

For credit-based flow control, the link partner input buffer can bedivided into eight buffer classes. Each SQ 330 can be assigned to one ofthese 8 buffer classes. Credits are maintained for each of the bufferclasses with each credit representing 32 bytes of storage in the linkpartner input buffer. In order to allow credit-based flow control towork with various devices (switch, enhanced NIC), each of which may havedifferent cell sizes, the cell size is a programmable value in units of32 bytes.

There may be two sets of VCs with each SQ 330 assigned to one set. Amaximum frame size worth of space can be reserved for each VC, and eachVC set can have a different maximum frame size. The remainder of thelink partner input buffer is shared dynamic space usable by any SQ/VC,subject to per VC and buffer class limits.

The size that comes with the request represents the size of the packeton the wire which includes a 4-byte FCS. This gets converted to aninternal 2-byte FCS at the link partner before writing the packet to thelink partner input buffer so the crediting needs to account for thisdifference, which can be a factor at the boundary of the cell size. Forinstance, for a 96 byte cell, a size that is 97 or 98 will take a singlecell. In order to know when this happens, the request includes acorrection term which is calculated as: req.len_correct=(byte_len %16)==1 or 2.

Further validation of this term is required to convert it to whateverthe cell size boundary may be. It will be valid when the length justexceeds the cell size. With this, the validated fen_correct term can bedetermined by: len_correct=(((16-byte size) % (2*32-byte cell size))==1)& req. len correct

An example of how these values work for a few cell and packet sizes isillustrated in the table below:

Length Correct Calculation

len_correct Size Req Size Cell Size Modulo Credit (bytes) len_correct(16B units) (32B units) result len_correct Taken 64 0 4 2 0 0 2 65 1 5 21 1 2 66 1 5 2 1 1 2 67 0 5 2 1 0 3 96 0 6 3 0 0 3 97 1 7 3 1 1 3  9B 17 3 1 1 3 99 0 7 3 1 0 4 128  0 8 4 0 0 4 129  1 9 4 1 | 4 130  1 9 4 11 4 131  0 9 4 1 0 5

The size that comes with the request uses 8-byte units and the linkpartner input buffer cell size is a multiple of 32 bytes (32*y wherey=cell size from CSR). First, the 8-byte size is converted to a 16-bytesize (ROUNDUP((8-byte size)/2)). Also, the cell size is converted to 16byte units (2*y). Mathematically, the number of cells a request will usecan be calculated by: ROUNDDN(((16-bytesize)+2*y−1−len_correct)/(2*y))=# of cells

While a divide operation is possible in hardware, due to timing reasons,a divide operation cannot be done in the critical path of thearbitration. Instead, an alternate credit management is used. That is,credits are maintained in units of 32 bytes. When a request winsarbitration, the number of credits taken is adjusted by the maximumerror term (2*y−1) using the calculation: ROUNDDN(((16-bytesize)+2*y−1)/2)=Maximum 32 byte credits needed. Because this calculationoverestimates the credit required for the packet, on the followingclock, a modulo operation (X=(16-byte size) MOD 2*y, y=32-byte cell sizefrom CSR) van be performed to determine what the actual remainder is.This value along with the len_correct term are used to adjust the creditcounter. The formula used to create the adjustment value (adf_val) forXis: If (X==0) adj_val=y−1 else if (X==1 and fen_correct) adj_val=y elseadj_val=ROUNDDN((X−1)/2)

The table below illustrates a request credit example for 96 byte cellsshowing the values used across several packet lengths for the 96 bytecells of the switch input buffer (y=3).

Request Credit Example For 96-byte Cells

Packet Size Packet Size Credit Modulo Corrected (bytes) (16-byte units)Taken Result len_correct adj_val Credit Taken 48 3 4 3 0 1 3 64 4 4 4 01 3 80 5 5 5 0 2 3 96 6 5 0 0 2 3 97 7 6 1 1 3 3 98 7 6 1 1 3 3 99 7 6 10 0 6 128  8 6 2 0 0 6

If a request is filtered before being forwarded to the link partnerinput buffer, the output buffer logic returns the SQ and VC so they canbe used to return the credits to the appropriate credit counters. Nosize is required since the packet size is always the same, the length ofa reduction frame (69-byte or 16-byte size=5).

The local (master) side of the link maintains a count of the number ofpackets sent from each VC across both sets (8 total), a count of amountof packet (in 3 2-byte quantities) sent to each VC (4), and a count ofthe amount of packet (in 32-byte quantities) sent for each buffer class(8). The link partner (slave) side of the link maintains the same set ofcounts with them being sent over the link periodically. The differencebetween the master and slave counts is a count of the number of packetsin the link partner input buffer from each VC across both sets and acount of the amount of space (in 32-byte quantities) currently occupiedby each VC and each buffer class. A count is also maintained of thetotal amount of space used across all packets. A summary of the countersis as follows: master_vcx_cnt[4]/slave_vcx_cnt[4]—master and slavecounts of the number of packets sent to each VC in set X;master_vcy_cnt[4]/slave_vcy_cnt[4]—master and slave counts of the numberof packets sent to each VC in set Y;master_bc_cnt[8]/slave_bc_cnt[8]—master and slave counts of the amountof space occupied by each buffer class in units of 32-bytes;master_vc_cnt[4]/slave_vc_cnt[4]—master and slave counts of the amountof space occupied by each VC in units of 32-bytes;master-tot-cnt/slave-tot-cnt-master and slave counts of the total amountof space occupied in units of 32-bytes.

All counters are set to zero on a warm reset. They are also forced tozero when the link is in the draining state or when the DBG_RESET CSRbit to clear their state is set. The output buffer filter will steer areduction packet to something other than the path to the link partnerinput buffer. In this case, a signal can be returned along with the SQand VC of the packet. Again, the length is not required as the size ofthese packets is fixed. This information is used to adjust theappropriate master credit counts.

A request is allowed to participate in arbitration if either its VCcount is 0 (indicating its one statically assigned slot is available) orthere is space for a max sized frame in the dynamic space (subject tothe targeted buffer class and VC limits). There can be a singleprogrammable value for max frame size which is used across all VCs andSQs. The request validation for input buffer space can be addressedusing credit-based flow control.

Credit-based flow control can be used to divide a dynamic space in twoways, each independent of each other: first, based on a limit of howmuch dynamic space each of the four VCs can take; and second, based on alimit to how much dynamic space each of the eight buffer classes cantake. In both cases, the limits are set as a percentage of the availablespace. For a given packet, space should be made available in both itstargeted VC and buffer class. For instance, if each space has its limitset to 50%, if one is active, it has access to 50% of the buffer space,with two active, each space gets 37.5% ((50+50*0.5)/2), with threeactive, each space gets 29.2% ((75+25*0.5)/3), and so on. Also, thetotal space used by those spaces that are active can be limited to thegiven total (50%, 75%, 87.5%). Accordingly, the space allocated to eachvaries dynamically by how many are currently active. When an additionalone goes active it causes others that are active to give up some oftheir space which is then taken by the new one.

Like the division function discussed above, this function is implementedas a lookup table. For the VC space in this example, there are 16entries with each entry specifying the space available to each VC alongwith the total space available across all VCs. For the buffer classes,there may be 256 entries with each entry specifying the space availableto each buffer class along with the total space available across allbuffer classes. Space for each is expressed in 2048-byte units. Thedepth of each table is sufficient to cover all combinations of activemembers (VCs or buffer classes), with each being able to have anindependent setting for their percentages. With this, it is up tosoftware to program the values in the table according to how much totaldynamic space there is and what percentage each is allowed to takeacross all possible combinations. As more become active, each is allowedless space and the total available increases. Requests for spaces thatare above this limit, or in total above the total limit, are not allowedto take more dynamic space.

A VC or buffer class is considered active either if it has a request inan age queue, or if it has outstanding credits for link partner inputbuffer space. As an example, consider there are only 4 spaces (16 entrytable) with percentages set as SPACE0(50%), SPACE1(40%), SPACE2(30%),SPACE3(10%), and a total dynamic space of 16 KB. This results in thevalues, in quantities of 16-bytes presented in the buffer space exampletable below.

Buffer Space Example

Index SPACE3 SPACE2 SPACE1 SPACE0 Total 0 N/A N/A N/A N/A N/A 1 N/A N/AN/A 512 512 2 N/A N/A 410 N/A 410 3 N/A N/A 319 398 717 4 N/A 307 N/AN/A 307 5 N/A 250 N/A 416 666 6 N/A 255 339 N/A 594 7 N/A 202 270 337809 8 102 N/A N/A N/A 102 9 94 N/A N/A 469 563 10 94 N/A 377 N/A 471 1175 N/A 299 374 748 12 95 284 N/A N/A 379 13 78 234 N/A 389 701 14 80 239319 N/A 638 15 79 236 315 394 1024

As an example, the values in the row for index 7 are calculated as:Total %=0.5+(1−0.5)*0.4+(1−0.5−(1−0.5)*0.4)*0.3=0.79;SPACEO=(0.5/(0.5+0.4+0.3))*0.79*1024=337;SPACEI=(0.4/(0.5+0.4+0.3))*0.79*1024=270;SPACE2=(0.3/(0.5+0.4+0.3))*0.79*1024=202; Total=337+270+202=809

As noted above, and referring back to FIG. 2 , switches, such as switch202 may be used to create a switch fabric, where the switch ports 220may be configured to operate as either edge ports or fabric ports. Asalso noted above, switch 202 can support various network topologiesincluding but not limited to, e.g., dragonfly and fat-tree topologies.Networks can be thought of as comprising one or more slices, each havingthe same overall topology, although slices may differ with respect tohow each is populated. Nodes are connected to one or more ports on eachslice. When a network has multiple slices, and a node is connected tomore than one slice, the node is assumed to be connected at the samelocation in each slice.

Routing in the switch fabric may be controlled by a fabric routingfunction (FRF) implemented in switch 202. An example FRF component 400is illustrated in FIGS. 4A and 4B. It should be understood that aseparate instance of FRF component 400 may be implemented within inputlogic for each port of switch 202. Routing decisions made by FRcomponent 400 can be applied to those frames that are not already partof an established flow. It should be noted that FRF component 400 doesnot necessarily know whether or not a particular frame is associatedwith a flow, but rather makes an independent forwarding decision foreach fame presented at an input port. FRF component 400 may comprisefilters, tables, circuitry, and/or logic such as selectioncircuitry/logic to effectuate routing of data throughout a switch fabricas described herein. As illustrated, FRF component 400 includes atleast: a minimal ports selection component 402 (which includes a minimaltables component 402A), various ports filters (permitted ports filters,operational ports filters, busy ports filters); a preferred portsdiscrimination component 402B; pseudo-random down selectioncomponents/logic 402C; exception tables 404 (including an exception listtable 404A); operational ports component 406 that includes a globalfault table 406A; and a routing algorithm table 408. As illustrated inFIG. 4B, FRF component 400 may further comprise: a non-minimal portsselection component 410 that includes local non-minimal selectioncomponent 410A and global non-minimal selection component 410B); andoutput logic component 412 (which is part of a switch's output controlblock), which includes an adaptive selection component or logic 412A.FRF component 400 includes other components, and are described herein.

In particular, FRF component 400 determines a preferred port withpreferred ports discriminator 402B to forward each frame presented atthe input port based on: a received frame's destination fabric address(DFA); the frame's current routing state (where the frame is along itspath, and the path(s) it took to reach its current routing state); theswitch fabric routing algorithm and configuration; and load metricsassociated with the output port (the aforementioned preferred port towhich the frame is to be forwarded) using busy ports filters.

FRF component 400 may include a routing algorithm table 408 that may beembodied as a software configurable table that determines valid choicesbased on the frame's current routing state. Valid choices are decisionssuch as whether a local minimal, global minimal, local non-minimal, orglobal non-minimal path is allowed to be chosen for the frame's nexthop. The routing state includes information such as the VC the frame wasreceived on, and whether it is in the source, the destination, or anintermediate group. The routing algorithm table 408, along with theadaptive selection function or logic 412A (described below), alsodetermines the VC to be used for the frame's next hop.

Frame routing with unicast DFAs will be described as an example.However, it should be noted that the DFA of the routing request caneither be in unicast of multicast format. The unicast format can includea 9-bit global ID field (global_id), a 5-bit switch ID field(switch_id), and a 6-bit endpoint ID field (endpoint_id). The global IDcan uniquely identify a group within the network. Specifically, itidentifies the final group to which the frame must be delivered. Theswitch ID uniquely identifies a switch within the group identified byglobal ID. The endpoint ID field, together with the global ID and switchID identify the endpoint, connected to the edge of the network fabric,to which the frame is to be delivered. This field is mapped to a port orset of ports on the switch identified by global ID and switch ID.

The multicast format includes a 13-bit multicast ID field(multicast_id). This field is mapped by FRF component 400 to a set ofports on the current switch to which the frame is to be forwarded.

From this information, FRF component 400 determines an updated routingstate for the frame, which is then carried within the frame. Forexample, to effectuate routing in a dragonfly topology, a frame'scurrent state may be gleaned from the frame's VC (discussed above).Based on algorithmic switch fabric routing rules specified for theswitch fabric (the selection of which is described below), FRF component400 determines a particular VC to be used for the frame's next hop toavoid any deadlocks. Additional routing state information can beprovided depending on where the frame is along its path, e.g., whetherthe frame is in its source group, in an intermediate group, or in itsdestination group. It should be noted that FRF component 400 performsport filtering (described in greater detail below) using permitted portsfilter, operational ports filter, busy ports filters, etc. to determineif a preferred port to which a frame is to be forwarded is currentlyfaulty, busy, absent, etc.

Switch 202 distributes load information between switches. The FRFcomponent 400 receives the load measurement of and from its associatedoutput port. The FRF component 400 receives summary load informationfrom its associated input port for a neighboring switch. Each FRFcomponent 400 exchanges load information with all other FRF instanceswithin the same switch. FRF component 400 provides summary loadinformation to its associated output port for delivery to a neighboringswitch. Through the load distribution mechanism, each FRF component 400learns the load measured at each output port of its switch. As well,each FRF learns the summary load information for all neighboringswitches.

It should be noted that FRF component 400 can support framemulticasting. When a multicast DFA is received, FRF component 400determines a set of ports to which the frame associated with themulticast DFA should be forwarded. The set of ports can be determined byaccessing a lookup table that maps software-configured multicast fabricaddresses to output ports. This helps avoid problems associated withduplicate multicast frame copies.

FIG. 5 illustrates an example route selection process involvingdown-selection of candidate ports and adaptive route selection based onload. FRF component 400 considers three categories of candidate ports towhich a frame may be forwarded: preferred minimal path candidate ports502; non-preferred minimal path candidate ports 504; and non-minimalpath candidate ports 506. Depending on where a frame may be along itspath, non-minimal path candidate ports are either global, non-minimalpath candidate ports or local non-minimal path candidate ports.

Filtering may be applied to the three categories of candidate ports,e.g., operational port filtering, useable port filtering, and busy portfiltering. Port filtering as applied herein can be used to reduce theset of valid ports considered as path candidate ports by identifying andremoving absent and/or faulty ports and/or busy ports fromconsideration.

Operational port filtering (or non-operational port filtering) can referto the removal of non-operational ports from sets of ports beingconsidered as candidates for routing, e.g., preferred minimal pathcandidate ports 502, non-preferred minimal path candidate ports 504, andnon-minimal path candidate ports 506. That is, switch 202 may identifycertain ports as being non-operational. These non-operational ports maybe reported in a non-operational port mask. It should be noted that insome embodiments, software can force additional ports of switch 202 tobe considered as non-operational using a non-operational port CSR, e.g.,when a port(s) is to become disconnected as a result of plannedmaintenance.

Usable (or unusable) port filtering may involve filtering out candidateports for consideration that would normally have been acceptable, butdue to faults within network 100, for example, the candidate ports havebecome unacceptable/unusable for reaching one or more destinationswitches, destination groups (of switches), etc., but remain acceptableor usable for reaching one or more other destination switches. In someembodiments, global fault table 406A can be used to block global minimalpath port candidates and global non-minimal path port candidatesdepending on a destination group of the frame being routed. For example,candidate ports that lead to an intermediate group (of switches) withoutconnectivity to a particular destination group (of switches) can beexcluded from consideration when routing frames to that destinationgroup, although the same candidate ports may not necessarily be blockedout for other destination groups. The global fault table 406A can bedetermined or indexed by the global_id field of the frame's DFA.

In some embodiments, an exception list maintained by exception listtable 404A may be used to conditionally exclude port candidatesdepending on the destination group or switch to which the frame is beingrouted. It should be noted that exception list table 440A may be used toidentify preferred global minimum path ports. Accordingly, use of theexception list table 404A to exclude port candidates is done when it isnot being used to identify preferred global minimum path ports.

It should be noted that knowledge regarding which ports are busy in aneighboring switch can be used to determine if the ports that connect toa neighboring switch are poor candidates to receive a frame based onwhether the neighboring switch will subsequently need to forward theframe to a port that is already busy. For example, when consideringcandidate ports for use in global minimal routing, the ports connectedto a neighboring switch are poor candidates if the neighboring switch'sglobal ports that connect to the frame's destination group are all busy.Similarly, when in the destination group and considering candidate portsfor use in local non-minimal routing, the ports connected to aneighboring switch are poor candidates if the neighboring switch's localports that connect to the frame's destination switch are all busy.

Accordingly, busy port filtering can be performed by FRF component 400by using busy port masks to remove heavily loaded ports from beingconsidered candidate ports. It should be noted that in some embodiments,heavily loaded ports are removed from consideration when other candidateports that are not heavily loaded exist. Otherwise, when non-heavilyloaded ports do not exist, busy port filtering will not remove theheavily loaded ports from consideration. FRF component 400 maintainsfour masks of busy ports, that is, ports whose load exceeds asoftware-defined threshold: local switch busy port mask; globalnon-minimal busy global port mask; global non-minimal busy local portmask; remote switch busy port mask. The remote busy port mask and otherload information is communicated between switches to populate the remoteswitch.

A local switch busy port mask can be applied to minimal path candidateports as well as to local non-minimal path candidate ports. The FRFgenerates a 64-bit Is_busy_port_mask by comparing each port's local_loadto a software defined threshold.

Ports with loads higher than this threshold are marked as busy in thismask.

A global non-minimal busy port global mask can be applied to globalports of global non-minimal path candidate ports. The FRF generates a64-bit gnmbgp_mask by comparing each port's gnmgp_load to a softwaredefined threshold. Ports with loads higher than this threshold aremarked as busy in this mask.

A global non-minimal busy local port mask can be applied to local portsof global non-minimal path candidate ports. The FRF generates a 64-bitgnmblp_mask by comparing each port's gnmlp_load to a software definedthreshold. Ports with loads higher than this threshold are marked asbusy in this mask.

A destination group dependent busy-port mask, obtained from a remoteswitch busy global port table can be applied to global minimal pathcandidate ports. Correspondingly, when a frame is being routed in itsdestination group, a destination switch-dependent busy-port mask,obtained from a remote switch busy local port table can be applied tolocal non-minimal path candidate ports.

Upon applying the aforementioned filtering or down-selection stage, aset of surviving path candidate ports 508 can result. That is, a reducednumber of candidate ports can be determined after removingnon-operational and unusable heavily loaded port candidates a set ofpath candidate ports remains. In some embodiments, a pseudo-randomselection process is used to further reduce the number of surviving pathcandidate ports 508 to a determined threshold number of ports associatedwith each category of candidate ports (preferred minimal path candidateports, non-preferred minimal path candidate ports, and non-minimal pathcandidate ports). In some embodiments, that threshold number ofcandidate ports may be four candidate ports per category. If the minimumthreshold number of candidate ports is not met, no candidate ports fromthat category are removed from consideration.

In some embodiments, this pseudo-random selection (or down selection) ofcandidate ports can be weighted. As will be described below, thisweighting can be applied to counteract a potential bias in thedistribution of globally non-minimal traffic among a group's globallinks. That is, weights, e.g., weights between 0 and 15, can be assignedto each port per the CSR configuration. This weighting can be used toinfluence the probability with which individual candidate ports arechosen such that higher-weighted ports have a great chance of beingchosen. For example, a weight of 15 results in a port having 15 timesgreater likelihood of being selected in the pseudo-random selectionprocess. In some embodiments, candidate ports may be filtered into fourgroups (GW1, GW2, GW4, GW8) based on their assigned weights, where acandidate port can belong to multiple groups depending on the assignedweight (e.g., a candidate port with weight 1 belongs only a one weightgroup, while a candidate port with weight 5 belongs to two groups (GW1and GW4, i.e., 1+4=5), and a candidate port with weight 15 belongs toall four groups (Gw1, GW2, GW4, GW8, i.e., 1+2+4+8=15). The number ofcandidate ports in each group can be determined (nW1, nW2, nW4, nW8),and pseudo-random selection is applied to each group to select onecandidate port from each group (cW1, cW2, cW4, cW8). The weight of eachgroup can be computed, along with their total weight: wW1=nW1;wW2=2*nW2; wW4=4*nW4; wW8=8*nws; wtotal=wW1+wW2+wW4+wW8. A fifthpseudo-random selection can be performed to choose a number j in therange O . . . Wtotal−1. One of the candidates, cW1, cW2, cW4, cW8 ischosen as the down selected candidate port based on the value of j asfollows: If j<wW1, choose cW 1; else If j<wW1+wW2, choose cW2; else Ifj<wW1+wW2+wW4, choose cW4; else choose cW8.

It should be noted that the same candidate port may be chosen by morethan one of the instances/iterations of the weighted pseudo-random downselection logic 410C, in effect reducing the number of candidates portsthat are chosen. The probability of the same candidate port being chosenby more than one of the mgnm=4 global non-minimal, weightedpseudo-random selectors decreases with increasing numbers of candidatesports to choose from. In the context of a dragonfly topology, forexample, and a network with full global bandwidth, at an edge port inthe source group there are potentially about 48 possible globalnon-minimal candidates ports: 16 global ports and 32 local ports. If alocal hop has been taken, the next hop is a global hope, therebyreducing the number of candidate ports to about 16. However, if thenetwork is tapered such that it only supports one quarter of full globalbandwidth, there may only be 4 global candidates to choose from after alocal hop has been taken.

FRF component 400 can use received remote switch busy port masks togenerate the aforementioned Remote Switch Busy Global Port Table of busyport masks that identify ports connected to neighboring switches thatshould be avoided as global minimal path candidates based on thedestination group to which the frame is being routed. Similarly, thereceived remote switch busy port masks can also be used to generate theaforementioned remote switch busy local port table of busy port masksthat identify ports connected to neighboring switches that should beavoided as local non-minimal path candidates, when routing in thedestination group, based on the destination switch to which the frame isbeing routed.

The rs_busy_port_masks are used in assessing the suitability ofneighboring switches (whether ports of neighboring switches are busy orquiet) for reaching specific destination groups via global minimal pathsand specific destination switches via local nonminimal paths or vialocal minimal paths. Each FRF instance corresponding to a local port ora global port can be configured to generate a 64-bit rs_busy_port_mask.The generated mask is delivered to the partner switch connected to thatport. Similarly, the partner switch can also generate and return anrs_busy_port_mask.

Each FRF instance communicates the rs_busy_port_mask, that it receivedfrom its partner switch, to the FRF instances in all of the switch'sother ports using the port status ring. The port status ringcommunicates load and status information between all the FRF instancesin the switch. Each FRF instance captures all rs_busy_port_masks suchthat all FRF instances learn the remote busy port status being providedby all neighboring switches. Each FRF instance uses thers_busy_port_masks that it receives to generate the Remote Switch BusyGlobal Port (RSBGP) Table and Remote Switch Busy Local Port (RSBLP)Table.

Generation of the rs_busy_port_mask is a two-step process. The firststep is to compare each port's local_load to a software configurablethreshold generating an intermediate mask of all ports that areindividually busy. Ports that are classified as non-operational are alsorecorded as busy in the intermediate mask. The second step takes linkbundling into account such that a port is only marked as busy in thers_busy_port_mask if it and all other ports, that are part of the samebundle, are marked as busy in the intermediate mask. Either all portsthat are members of the same bundle are marked as busy in thers_busy_port_mask, or none are. Global ports that are part of the samebundle all connect to the same remote group. Local ports that are partof the same bundle all connect to the same remote switch within thecurrent group.

As the rs_busy_port_masks are used to determine whether the switch thatgenerated the mask is a good candidate for routing a frame to anothergroup or to another switch in the current group, bundling is used toprovide a consistent view of the generating switch's suitability whenthe busy status across its links, that connect to the destination groupor to the destination switch in the current group, is inconsistent. Therationale for the treatment of bundling described here is that theswitch generating the rs_busy_port_mask remains a candidate for reachingthe destination group, or the destination switch in the current group aslong as it has at least one link to the destination group or switch thatis not busy; adaptive routing at the switch that generated the rs_busyport_mask should direct the frame to the non-busy link.

Ports must be included in either the bundled ports mask CSR or theunbundled ports mask CSR (both of which are part of the staticdescription of the wiring) in order for them to be marked as busy in thers_busy port_mask. The bundled port masks are scanned to identify thebundles and the ports that they contain. In addition, the unbundled portmask is consulted to identify any other ports, that are not members of abundle, but whose busy status should also be included in the generatedrs_busy_port_mask.

A different software-defined threshold is used in computing thers_busy_port_mask because of the larger latency involved incommunicating and processing the rs_busy_port_mask and in delivering aframe subject to this mask to the remote switch that generated the mask.Because of the larger latency, it may be useful to require a port to bemore loaded before it is considered to be so busy that it is not a goodcandidate for receiving additional frames from a remote switch. A busyremote port should be sufficiently loaded such that it remains loadedthroughout the time it would take to receive a frame that has beensubject to the mask.

The aforementioned RSBGP table stores busy port masks indexed bydestination group (global_id). It is populated dynamically usinginformation contained in received rs_busy_port_masks together withtopological information about the system stored in configuration state.Again, the RSBGP table is used in the evaluation of global minimal pathsconsisting of a hop to a neighboring switch which has a global portconnected to the destination group to filter out ports of the currentswitch which are poor choices for use in reaching the destination groupbecause the corresponding global port or ports, of the neighboringswitch reached by the filtered-out ports of the current switch, are tooheavily loaded.

The RSBLP table stores busy port masks indexed by destination switch(switch_id), and again, can be used in the evaluation of localnon-minimal paths consisting of a local hop to a neighboring switchfollowed by another local hop to the destination switch. It is populateddynamically using information contained in received rs_busy_port_maskstogether with topological information about the system stored inconfiguration state. For topologies, such as fat-tree, where a localminimal path can consist of a local hop to a neighboring switch followedby another local hop to the destination switch, the RSBLP Table can alsobe used in the evaluation of local minimal paths. The RSBLP table isused to filter out ports on the current switch which are poor choicesfor use in indirectly reaching the destination switch because theneighboring switch's port or ports that connect to the destinationswitch are too heavily loaded.

It should be noted that the RSBGP table and the RSBLP table are neverboth accessed for the same routing request. The former is accessed whenrouting a frame that is not in the destination group, and the latter isaccessed only when routing a frame that is in the destination group.Therefore, both can be implemented within the same memory, termed theRemote Switch Busy Port Table.

A Busy Ports Filter is used to remove candidate minimal path ports thatare poor choice because they lead to heavily loaded paths. Separatecopies of the Busy Ports Filter are applied independently to thepreferred and to the non-preferred minimal path ports. If global minimalrouting is enabled a first stage of this filter removes ports marked asbusy in the indexed entry of the Remote Switch Busy Global Port Table.If in the destination group and local minimal routing is enabled, anoptional first stage of this filter removes ports marked as busy in theindexed entry of either the Remote Switch Busy Local Port Table or theRemote Switch Busy Global Port Table, with the table that is used beingbased on CSR configuration. The first stage of this filter is notapplicable and not used with the Dragonfly topology when in thedestination group; however, it can be applicable to other topologiesincluding fat tree. A second stage of this filter removes ports markedas busy in the aforementioned Is_busy_port_mask. If no candidates remainafter the second filter stage, the second filter stage is disabled suchthat the only candidates ports that remain, if any, will be seen to havea high load in the Adaptive selection stage.

A Local Non-Minimal Busy Port Filter is used in the destination group toremove local non-minimal candidate ports that are poor choice becausethey lead to heavily loaded paths. A first stage of this filter removesports marked as busy in the indexed entry of either the Remote SwitchBusy Local Port Table or the Remote Switch Busy Global Port Table, withthe table that is used being based on CSR configuration. A second stageof this filter removes ports marked as busy in the aforementionedIs_busy_port_mask. If no candidates remain after the second filterstage, the second filter stage is disabled such that the only candidatesports that remain, if any, will be seen to have a high load in theAdaptive selection stage.

A Global Non-Minimal Busy Port Filter is used when global non-minimalrouting is enabled to remove candidate global non-minimal path portsthat are poor choice because they lead to heavily loaded paths.Specifically, global ports marked as busy in the aforementionedgnmbgp_mask are removed and local ports marked as busy in theaforementioned gnmblp_mask are removed. If no candidates remain afterapplication of these masks, both masks are disabled such that the onlycandidates ports that remain, if any, will be seen to have a high loadin the Adaptive selection stage.

Provided that there is at least one valid candidate port, the variousbusy port filters (Busy Ports Filter, Local Non-Minimal (LN) Busy PortFilter, Global Non-Minimal (GN) Busy Port Filter) may not be allowed tocollectively block all candidate ports. If there are viable candidateport choices, they are allowed, despite being “poor” choices, if thereare no better choices. Otherwise, an empty route response will begenerated for the routing request when routes are actually available.

To prevent an incorrect empty route response from being generated, thefirst stage of the preferred and non-preferred minimal path busy portfilters (FIG. 4A) and the first stage of the local non-minimal path busyport filter (FIG. 4B) are all disabled if the following conditions areall true: No candidates survive the first stage of the preferred minimalpath busy port filter (Busy Ports Filter); No candidates survive thefirst stage of the non-preferred minimal path busy port filter (BusyPorts Filter); No candidates survive the first stage of the localnon-minimal busy port filter (Local Non-Minimal (LN) Busy Port Filter);and No candidates survive the global non-minimal busy port filter(Global NonMinimal (GN) Busy Port Filter).

It should be noted that there will be no minimal path candidate ports ifminimal routing is disabled (Permitted Ports Filter). There will belocal non-minimal path candidate ports only if local non-minimal routingis enabled (Candidate Local Non-Minimal Path Ports). There will beglobal non-minimal path candidates only if global non-minimal routing isenabled (Candidate Global Non-Minimal Path Ports). Local and globalnon-minimal routing are generally not both enabled simultaneously. Whenthe first stage of the preferred and non-preferred minimal path busyport filters and the local non-minimal busy port filter are disabled dueto the conditions described above, the only candidate ports that will beseen at an adaptive selection stage (described below) will be poorcandidates because they will all be ports that lead to other switcheswhose ports (that connect to the destination group or to the destinationswitch) are heavily loaded. This is because these are the only candidateports that were being blocked by the filters that are being disabledand, without these filters being disabled, there are no othercandidates.

The adaptive selection stage will choose between theseremaining/surviving candidate ports, which are all poor, based on theirbiased local loads, although their local loads will not necessarilyreflect the reason why they are poor. Their poor character can be theresult of high downstream load on certain ports of the other switchesreached by these candidate ports. It is because the adaptive selectionstage may not be able to see how poor these candidates are that thecoordination between the different busy port filters, described hereinmay be used. If each busy port filter decides independently whether ornot to disable its RSBGP Table and RSBLP Table-based filters, situationssuch as the following could occur. The non-preferred minimal path busyport filter might produce one or more candidates, which are not poor,without any of its filter stages disabled. The preferred minimal pathbusy port filter might only be able to produce one or more candidateports by disabling both of its filter stages. Thus, all of the candidateports it is able to produce are poor. At the adaptive select stage, thedown-selected, not poor, non-preferred minimal path candidate ports, arecompared against the down-selected, poor, preferred minimal pathcandidate ports. However, the adaptive selection stage lacks visibilityinto how poor the preferred minimal path candidates are, so it mayselect a poor preferred minimal path candidate over a not poornon-preferred minimal path candidate.

An alternative to the busy port filter coordination mechanism describedherein, would be for all of the busy port filters to act independently,but for the minimal path and the local non-minimal path busy portfilters to each forward a signal through to the adaptive select stage toindicate if their respective candidate ports are poor choices due tobusy ports at downstream switches. If they are, the adaptive selectionfunction may de-prioritize their candidate ports in favor of otherports. The result would be the same as is achieved by the coordination,described herein, between the various busy port filters.

As illustrated in FIG. 5 , load-based adaptive selection can beperformed on the surviving path candidate ports 510 that remain afterthe pseudo-random selection process is performed by FRF component 400.The adaptive selection stage will result in a single, least loadedcandidate port 512 to which a frame can be routed, where the currentload present on the candidate ports surviving pseudo-random downselection (surviving path candidate ports 508) are compared to determinethe least loaded candidate port among this remaining set of candidateports.

In some embodiments, preferred minimal path candidate ports arepreferentially selected over non-preferred minimal path candidate ports,and minimal path candidate ports are to be preferentially selected overnon-minimal path candidate ports. To accomplish this preferentialselection, a bias value can be added to each candidate port's loadbefore the adaptive selection comparison is performed. The bias valueused can be configured using CSRs, and can vary depending on the type ofpath to which it is being applied (i.e., non-preferred minimal,preferred minimal, an non-minimal), the traffic class of the frame beingrouted, and where the frame is along its path. For example, framesbelonging to a low-latency traffic class can be more strongly biasedtowards minimal paths versus frames in other traffic classes to have agreater likelihood of achieving/comporting with low-latency requirementsor needs. Frames may also be increasingly biased towards minimal pathroutes the close the frames are to their destination.

In particular, load values represent the busyness of switch 202's portsand are used in evaluating the load-based port masks and in comparingcandidate ports during the adaptive route selection process. Load-basedport masks are used in the busy port filters to remove ports that arepoor candidates, based on current load, from the set of candidates beingconsidered. There are a number of different types of load values usedwithin the switch and some are communicated to neighboring switchdevices. These load values are described in the following sections,noting that FIG. 6 illustrates how the load values are measured,communicated, and used.

Several load metrics are computed and used in determining which port toroute a frame when there is more than one port to which the frame can berouted. The load metrics are also used in generating busy-port masks,which as described above, are used to remove heavily loaded ports fromconsideration.

There are five load metrics described herein: local load; group load;global non-minimal global port load; mean global load; and globalnon-minimal local port load.

Regarding local load, the load of each of a switch's output ports (e.g.,output ports 220 c of switch 202) is continuously being evaluated andprovided to the corresponding FRF instance as the 8-bit valuelocal_load. Larger values represent higher load. The current loadpresent at each output port is measured by the output control age queueblock. The output port load is provided by each age queue instance tothe FRF instance (of FRF component 400) that is associated with theinput side of the same port. The load value provided to the FRF is an8-bit value termed the local_load. The age queue determines the localload based on a combination of the amount of traffic enqueued, waitingto go out that port and the amount of traffic enqueued at the oppositeside of the link in the link-partner switch device's input buffer. EachFRF instance distributes the local_load value it receives from itsassociated age queue instance to all other FRF instances. In this way,each FRF instance learns the current local_load of every output port.

When the port loads of candidate ports are being compared to determinethe best port to route a frame to, it is the port's local_load valuethat is used for ports being considered for minimal path routing, andfor ports being considered for local non-minimal path routing.

Group load is a measure of how suitable a dragonfly group is for use asthe intermediate group in a global non-minimal path. The 8-bit groupload value is not computed by a switch, such as switch 202, but issoftware-configurable. Software might use a measure of the networkinjection load present across the input side of the group's edge portsin deriving the group_load value, or might determine the group_loadvalue based on a policy of discouraging use of certain groups asnon-minimal intermediate groups, perhaps based on the jobs or servicesthat are running in the groups. That is, the group_load value isintended to be representative of the amount of local traffic within agroup.

A network management stack sets the group_load value by periodicallywriting to a CSR. The software-configured group load value iscommunicated across global links. FRF instances associated with globallinks forward the group_load value that they receive from theirlink-partner in the group at the opposite side of the link, to all otherFRF instances in the switch. In this way, each FRF instance learns thegroup load values of the groups at the opposite end of each of theglobal links terminated by the switch.

In terms of global non-minimal global port load (gnmgp_load), this loadis a metric used in assessing a global port's suitability for use indirecting a frame to the intermediate group reached by the global linkconnected to the global port. The gnmgp_load is nominally equal to themaximum of the global port's local_load and the group_load value beingreceived from the group reached by the global link. However, through CSRconfiguration, the group_load component can be excluded.

When the port loads of candidate ports are being compared to determinethe best choice port to route a frame to, it is the port's gnmgp_loadvalue that is used for global ports being considered for globalnon-minimal path routing.

Mean global load (mean_global_load) is intended for use in assessing aswitch's suitability for use in reaching any intermediate group that isdirectly connected to that switch. The mean_global_load value is an8-bit value equal to the arithmetic mean of the gnmgp_load values of allof the switch's global ports. Ports that are classified asnon-operational by either hardware or software are excluded from thecalculation. The ports to include in the mean_global_load computationare determined from through CSR configuration.

For any port whose load is included in the mean_global_load computation,if a group_load value is not being received for that port, eitherbecause link partner data is not being received for that port or becausethe link partner data that is being received is not global link data,the contribution of that port to the mean_global_load is based solely onthat port's local load. The computed mean_global_load value iscommunicated across local links. FRF instances associated with locallinks forward the mean_global_load value, that they receive from theirlink-partner in the local switch at the opposite side of the link, toall other FRF instances in a switch. In this way, each FRF instancelearns the mean_global_load values of the local switches at the oppositeend of each of the local links terminated by the switch, and can usethese values in global non-minimal path selection.

Global non-minimal local port load metrics are computed by each FRFinstance. The global non-minimal local port load (gnmlp_load) is ametric for use in assessing a local port's suitability for use indirecting a frame to an intermediate group of a global non-minimal path.The global non-minimal local port load takes into account the load onthe local port as well as the suitability of the local group switch, towhich the port connects, for use in reaching an intermediate group. Aport's gnmlp_load value is equal to the maximum of the port's local_loadand the mean_global_load reported by the port's partner switch. Throughsoftware configuration it is possible to remove the mean_global_loadcomponent such that a port's gnmlp_load becomes simply equal to itslocal_load.

The gnmlp_load value is an 8-bit value. Each FRF instance computes thegnmlp_load value for all of its switch's ports at which link partnerdata for a local link is being received. If load status information isnot being received from a port's partner switch, the gnmlp_load valuefor that port is set equal to the port's local_load.

FIG. 6 illustrates example load measurements and how load measurementmay be exchanged between switches in a group. FIG. 6 illustrates a groupof switches, e.g., group 1, comprising switches 602, 604, and 606, eachof which may be embodiments of switch 202 (FIG. 2 ). Group load values,as noted above, can be exchanged across global links, and as shown,group_load values are transmitted from/received by each of switches 602,604, and 606 from other groups/switches in the switch fabric. Withingroup 1, switches 602, 604, and 606 exchange mean_global_load values.Switch 602 also is shown as computed gnmlp_load values at the outputside of local ports, based on local_load at that port, andmean_global_load reported by the link partner. Further still, local_loadvalues at the output of all ports are computed by switch 602. It shouldbe noted that mean_global_load and group_load values are sent acrosslinks between connected switches symmetrically from each switch to theother.

The fabric routing process described in the preceding subsections isperformed for every frame received. Switch determines whether to performpacket-by-packet adaptive routing (using the recommended port choice) orflow based adaptive routing (where is the port choice determined for thefirst packet in each flow is used for all packets in the flow) accordingto the ordering requirements of the traffic.

As has been described herein, a switch, such as switch 202 supportsminimal and non-minimal path routing. It should be understood thatminimal paths are based on the destination. If a destination NIC islocal, an output port that connects to the destination switch isselected. If the destination is in another group, the packet is routedto a switch within the local group that is connected to the destinationgroup. In a large system, there may only be one such path, but in asmall system there are likely to be many, some connected to the inputswitch and others to switches elsewhere within its group. The inputswitch selects between them.

The candidate ports considered for minimal path routing are furtherdivided into preferred and nonpreferred sets of ports where ports in thepreferred set may lead to a path containing fewer hops. Non-minimalpaths route packets via an intermediary switch, referred to as a rootswitch. Root switches are selected on a packet-by-packet basis or aflow-by-flow basis depending on the ordering requirements of thetraffic.

Non-minimal traffic is routed “up” to the root switch, and thenminimally “down” to the destination. In some embodiments, intermediateroot switches are selected at random so as to distribute load uniformly.The network, e.g., network 100, provides control over intermediate groupselection enabling traffic to be routed towards intermediate groups thatare known to be lightly loaded or away from those that have specificfunction or are known to be heavily loaded. Root switches may bedistributed over all groups, where a non-minimal path may detect a rootswitch in the source group, the destination group, or any intermediategroup. Global non-minimal routes take an indirect path through a rootswitch in an intermediate group. These paths require two global hops,one from the source group to an intermediate group, and one from theintermediate group to the destination group. Global non-minimal pathsrequire up to three local hops, one in each group. The maximum pathlength is normally five switch-to-switch hops, whatever the system size.Although unlikely, it is possible to employ up to two additional localhops to work around faults within the network.

Minimal routing is to be preferred as the paths are shorter, and hencethe load on the network is lower. However, minimal routing alone willresult in poor performance on some traffic patterns, for example whenall nodes in one group communicate with nodes in one other group.Achieving good performance across a wide range of traffic patternsrequires a mix of minimal and non-minimal routing.

At each hop along a frame's path, the routing modes that may be used toadvance the frame along its next hop are controlled by the configurationof the FRF routing algorithm table 408. When a frame is received at aswitch input port, the types of paths along with the frame may beforwarded is determined: local minimal, global minimal, localnon-minimal, and global non-minimal. The set of output ports to whichthe frame may be forwarded is determined by the type of paths allowed atthat point.

The types of paths that are allowed to be taken depends on where theframe is at along its journey between its ingress and egress ports ofthe network. The path types are as follows. Local minimal paths selectlinks that are directly connected to the frame's destination switch andmay be used when the frame is in its destination group. Global minimalpaths may be used when the frame is not in its destination group andselect either global links that directly connect to the frame'sdestination group or local links that connect to a switch that hasworking global links that directly connect to the frame's destinationgroup. Local non-minimal paths may be used when the frame is in itsdestination group, or when the frame is in an intermediate group. Localnon-minimal paths select local links connected to other switches in thegroup without regard for the frame's destination. When in thedestination group, it must be possible to reach the frame's destinationswitch within one more hop after taking the local non-minimal hop. Whenin an intermediate group, it must be possible to reach a switch with aworking global link that connects to the frame's destination groupwithin one more hop after taking the local non-minimal hop. Local links,that connect to switches from which this in not possible, must not beselected.

Global non-minimal-paths may be used when the frame is in its sourcegroup and is not in its destination group. Global non-minimal-pathsselect either global links connected to other groups or local linksconnected to other switches in the source group without regard for theframe's destination. Global links must only be selected if they connectto a group that has working links connecting it to the frame'sdestination group. Similarly, local links must only be selected if theyconnect to switches that have global links that are, themselves, validglobal non-minimal path choices.

Adaptive routing selects between minimal and non-minimal paths(described above) according to their current load.

In terms of minimal routing, when in the destination group, but not atthe destination switch, local minimal routes are generated by looking upthe switch_id field of the destination fabric address in a local switchminimal table (FIG. 4A). The lookup returns a set of valid links. Thelocal switch minimal table contains 128 entries each of 64 bits, witheach bit representing one possible output port. When at the destinationswitch, the egress port or port choices are generated by looking up theendpoint_id field of the destination fabric address in the local portminimal table. The lookup returns a set of valid links. The local portminimal table contains 64 entries each of 64 bits, with each bitrepresenting one possible output port.

Global minimal routes are generated by looking up the global_id field ofthe destination fabric address in a global minimal table (FIG. 4A). Thelookup returns a set of valid links. The global minimal table contains512 entries each of 64 bits, with each bit representing one possibleoutput port.

Local minimal paths take at most one switch-to-switch hop, from thesource switch to the destination switch, both of which are within thesame group. There can be several such paths. Local non-minimal pathstake two switch-to-switch hops, from the source switch to anintermediate switch, known as the Root switch, and from there to thedestination switch. There are many such paths.

Global minimal paths take one global hop from the source group to thedestination group. There is at most, one local hop in each of the sourceand destination groups. Global minimal paths require a maximum of threeswitch-to-switch hops whatever the system size.

In certain system configuration in which there are multiple global linksconnecting a source group to a destination group, a bias can arise suchthat the proportion of traffic injected at the source group that isdistributed to each of the global links is not equal. As an example,consider the case of switch A, B, and C, all in the group X, with switchB having three global links connecting it to group V and switch C havingtwo global links connecting it to group V. If traffic injected at switchA, destined for group V, is equally distributed between switch Band C,each of the two global links of switch C will be more heavily loadedthan each of the three global links of switch B.

To enable the bias to be counteracted, the Global Minimal Table can bedivided into several blocks, each of which is capable of generating avalid set of global routing choices for any destination group. On aframe by frame basis, the block that is used to service the request ispseudo-randomly selected by the FRF. Within each Global Minimal Tableblock instance, only a subset of the possible candidate ports that canbe used to reach the destination group are populated. The subset ischosen in such a way so as to counteract the bias. The populated subsetscan be varied across the different block instances such that allpossible candidate ports are able to be used.

A global minimal path between an edge port in one group and an edge portin another group can require one, two, or three hops across fabriclinks. One hop if the switch containing the ingress edge port in thesource group has a global link directly connecting it to the switchcontaining the egress edge port in the destination group. Two hops ifthe frame traverses a global link between the two groups that isconnected directly to either the ingress switch in the source group orto the egress switch in the destination group. In this case, one hopacross a local link in either the source group or the destination groupis also required. Lastly, three hops are required if the frame traversesa global link that is not directly connected to either the ingressswitch in the source group or to the egress switch in the destinationgroup. In this case, a hop across a local link is also required in boththe source and destination groups. The local link hop in the sourcegroup takes the frame from the ingress switch to the source group switchthat is connected to the global link. The local link hop in thedestination group takes the frame from the destination group switch thatis connected to the global link to the egress switch.

When identifying minimal path candidate ports, the FRF is able toclassify the candidates into a set of preferred ports and a set ofnon-preferred ports. The preferred ports are those that allow a globalminimal path requiring two, or fewer fabric link hops. The non-preferredports are all of the minimal path candidates that are not classified aspreferred. Use of preferred paths, when available, and when not tooheavily loaded reduces the average load on the system's local fabriclinks as it reduces the average number of local fabric links traversedper frame. Use of a preferred path may also reduce the end-to-end fabriclatency experienced by the frame.

When performing local non-minimal routing, any local link can be acandidate. However, some local links may need to be excluded fromconsideration if they lead to a switch from which it may not be possibleto reach the destination because of link or switch failures that existwithin the system. A CSR controls which ports are candidates for localnon-minimal path routing.

When performing global non-minimal routing, generally any global linkcan be a candidate. Additionally, generally any local link that reachesa switch with operational global links can also be a candidate. However,some links may need to be blocked from consideration if they lead to aswitch or to a group from which it may not be possible to reach thedestination group because of link or switch failures that exist withinthe system. CSRs control which ports are candidates for globalnonminimal path routing.

When selecting a candidate port to use for global non-minimal routing,if all candidate ports, global and local, are equally likely to beselected, for many system configurations globally non-minimal trafficwill not be evenly distributed among the global links leaving the group.Consider, for example, the situation of three switches, A, B, and Cwithin a group, where each switch is connected to each other switch byfour local links, and switch A and switch Beach terminate 14 globallinks and switch C terminates 16 global links. Ingress traffic arrivingat an edge port of switch A may be routed globally non-minimally to anyof the global or local links terminated by switch A. If it is equallylikely to be routed to any of these links, then each global linkterminated by switch B will receive only 4/14th (4 local links reaching14 global links) of the traffic routed to each global link terminated byswitch A. Similarly, each global link terminated by switch C willreceive 4/16th (4 local links reaching 16 global links).

To counteract this potential bias in the distribution of globallynon-minimal traffic among a group's global links, when the set of globalnon-minimal candidate ports is being pseudo-randomly down selected tothe small number of ports that will participate in the adaptive routingstage, a weighting can be applied to each of the candidate ports suchthat some will be more likely than others to survive the down-selectionprocess.

Adaptive routing selects between these minimal and non-minimal pathsbased on their load. Adaptively routed traffic starts on a minimal path,diverting to a non-minimal path if the load on the minimal path is high(this is known as progressive adaptive routing). Such paths are said tohave diverged.

A non-minimal path can be selected at the injection point or at the exitrouter in a source group. A local non-minimal route may be taken withinthe source group, an intermediate group, or a destination group.Dragonfly routing algorithms allow a non-minimal path in both theintermediate and destination groups (consider a case where all trafficincoming on the global ports of a particular switch is destined for NICson another switch in the group). In general however, non-minimal trafficis sufficiently well distributed as to avoid this happening, but anadditional hop in the destination group may still be beneficial in caseswhere there is an error on a local link. Having arrived at theintermediate group the packet may take either a minimal route to thedestination group or a local non-minimal route to a switch with a pathto the destination group.

Again, this decision is made based on load. Having taken a hop withinthe intermediate group the packet must detect root and take a minimalpath to the destination. Adaptive decisions are made based on load and abias towards preferred minimal, non-preferred minimal, or non-minimal. Arouting algorithm, as described above, increases the bias towardsminimal paths the closer a packet is to its destination. This algorithmprefers a direct path across the intermediate group provided the load islow.

Restricted routing is used at points other than injection and rootdetection to prevent packets from flowing back in the direction fromwhich they came. In a switch, cases in which a packet has taken one hopfrom points of injection and root detection are detected and ensuredthat a global port is taken. For local minimal routing, having taken ahop from the root, the packet will arrive at a switch that is connectedto the destination NIC. For global minimal routing, having taken a hopfrom the point of injection, the packet will arrive at a switch with aglobal link, which must be taken. In the intermediate group, packets areallowed to take a local hop at the point of injection. From that pointonward, the packet must follow a minimal path to its destination.

When passing information from switch to switch, it is necessary to makeinstantaneous decisions about the next hop on the path. Decisions aretaken using information derived from local state and information that iscommunicated from neighboring switches. Use of information from manydifferent sources allows for more accurate/effective decisions. Thisincludes information from neighbors.

Prior systems carried information on average load from switch to switch.That said, more detailed information from related or neighboringswitches is more helpful. In the current switch ASIC, a set of valuescan include information indicative of the status of output ports ofrelated/neighboring switches. By passing this set of values, much betterrouting decisions can be made. In one example, a flag is passed backfrom neighboring switches, with the flag having one bit for each outputport. For example, with a switch having 64 outputs, a 64 bit flag wouldbe transmitted. This is much more accurate than simply passing a globalaverage for neighboring ports.

FIG. 7A illustrates an example scenario where average load is used as abasis for routing packets in switch fabric comprising source switch 702,destination switch 708, and two possible intermediate switches 704 and706. As illustrated in FIG. 7A, source switch 702, based on adaptiverouting as described herein, may determine two candidate intermediateswitches (704 and 706) through which packets may be routed from sourceswitch 702 to destination switch 708. When basing adaptive routingdecisions on average load of the intermediate switches 704 and 706, inthis example, intermediate switch 704 may have an average load value oftwo, while intermediate switch 706 may have an average load value ofthree. Basing adaptive routing decisions on average load value wouldthen result in source switch 702 selecting to reach destination switch708 by way of intermediate switch 704 (i.e., route or path 710).However, the link between intermediate switch 704 and destination switch708 may be busy, which as noted above may negatively impact, e.g.,latency.

In accordance with one embodiment, and as described above, port busynesscan be taken into account. That is, and referring back to FIG. 5 ,down-selection of candidate ports and adaptive route selection can bebased on load. Again, FRF component 400 considers three categories ofcandidate ports to which a frame may be forwarded: preferred minimalpath candidate ports 502; non-preferred minimal path candidate ports504; and non-minimal path candidate ports 506. Depending on where aframe may be along its path, non-minimal path candidate ports are eitherglobal, non-minimal path candidate ports or local non-minimal pathcandidate ports.

Filtering may be applied to the three categories of candidate ports,e.g., operational port filtering, useable port filtering, and busy portfiltering. Port filtering as applied herein can be used to reduce theset of valid ports considered as path candidate ports by identifying andremoving absent and/or faulty ports and/or busy ports fromconsideration.

In the example of FIG. 7B, busy port filtering may result in a differentpath being selected to route frames from source switch 702 todestination switch 708. Again, knowledge regarding which ports are busyin a neighboring switch (in this example, intermediate switches 704 and706) can be used to determine if the ports that connect to a neighboringswitch are poor candidates to receive a frame based on whether theneighboring switch will subsequently need to forward the frame to a portthat is already busy. Accordingly, busy port filtering can be performedby FRF component 400 by using busy port masks to remove heavily loadedports from being considered candidate ports. FRF component 400 maintainsfour masks of busy ports, that is, ports whose load exceeds asoftware-defined threshold: local switch busy port mask; globalnon-minimal busy global port mask; global non-minimal busy local portmask; remote switch busy port mask. Information from these masks iscommunicated between switches to populate the remote switch.

Here, a local switch busy port mask can be applied to minimal pathcandidate ports as well as to local non-minimal path candidate ports,e.g., output ports of intermediate switches 704 and 706. FRF component400 generates a 64-bit Is_busy_port_mask by comparing each port'slocal_load to a software defined threshold. Ports with loads higher thanthis threshold are marked as busy in this mask. In this example, outputports from intermediate switch 704 directed to destination switch 708meet or surpass the software defined threshold specified for the switchfabric. Therefore, the Is_busy_port_mask indicates that the link fromintermediate switch 704 to destination switch 708 is busy. On the otherhand, the output ports of intermediate switch 706 to destination switch708 are not marked or flagged with the Is_busy_port_mask as the busynessthreshold is not met/surpassed, reflecting that the link betweenintermediate switch 706 and destination switch 708 is quiet, and notbusy.

Based on the busy port mask indication that the link betweenintermediate switch 704 and 708 is busy, the output port of intermediateswitch 704 linked to an input port of destination switch 708 is deemedto be a poor candidate, and removed from consideration. Accordingly, andin contrast to the scenario of FIG. 7A, where route 710 is selectedbased on average load, route or path 712 is selected to route a frame(s)from source switch 702 through intermediate switch 706, and on to itsdestination, i.e., destination switch 708. It should be understood thatthe quiet link condition between intermediate switch 706 and destinationswitch 708 is a better choice to route frames from source 702 despitethe average load being higher.

Similarly, as noted above, FRF component 400 can use received remoteswitch busy port masks to generate the aforementioned Remote Switch BusyGlobal Port Table and Remote Switch Busy Local Port Table of busy portmasks that identify ports connected to neighboring switches that shouldbe avoided as global minimal path candidates based on the destinationgroup to which the frame is being routed and that should be avoided aslocal non-minimal path candidates based on the destination switch towhich the frame is being routed. Thus, the rs_busy_port_mask can also beused to identify ports connected to neighboring switches that may bebusy or quiet in accordance with some embodiments. In the example, ofFIG. 7B, an input port of destination switch 708 may be deemed busy byway of rs_busy_port_masks applied thereto. Such ports may be avoided aslocal non-minimal path candidates, when routing in the destinationswitch, based on the destination switch to which the frame is beingrouted

FIG. 8 is a flow chart illustrating example operations that may beperformed to effectuate adaptive route or path selection in accordancewith one embodiment of the disclosed technology. As noted above, switch202 may be an ASIC, and thus one or more electronic circuits thatinclude electronic components are provided for controlling orinstantiating FRF component 400 (FIGS. 4A and 4B) by performing thedisclosed example operations.

At operation 800, a plurality of load signals from a plurality ofneighboring switches is received, each of the plurality of load signalscomprising a set of values indicative of a load at each of the pluralityof neighboring switches providing the load signal, each value within theset of values providing an indication for each link of the plurality oflinks attached thereto as to whether the link is busy or quiet. Asdescribed above, a switch, e.g., switch 202 may have a plurality ofports (64 ports in some embodiments). Packets may be routed betweeninput and output ports of one switch to another one or more switches(each having their own input and output ports. Routing of packetsbetween switches can be performed in accordance with certaincharacteristics of the switches that the packets may traverse along apath from a source switch to a destination switch.

Between the source and destination switches may be one or moreintermediate switches. In order to select a path, ports of switches overwhich the packet may traverse are filtered to identify certain pathcandidate ports that have desirable characteristics regarding, e.g., howbusy they are in terms of traffic traversing through the ports.Accordingly, adaptive routing is effectuated by determining, based onload (an indication of busyness) associated with a candidate port,whether or not the packet should traverse path including a candidateport of a switch, such as an intermediate switch. In some embodiments,the local load is compared to a threshold that can be specified by theCSR configuration, and ports can be excluded based on whether or not thelocal load falls below or surpasses that threshold.

At operation 802, based upon the plurality of load signals, an outputlink is selected for routing a received packet and routing the receivedpacket via the selected output link. That is, a mask can be applied tothose ports whose local load surpasses the threshold, i.e., those portsare marked as being busy in this mask. It should be understood thatother busy port masks can be applied in accordance with otherembodiments, e.g., global non-minimal busy global port mask, globalnon-minimal busy local port mask, or a destination group dependentbusy-port mask depending on the circumstances. For example, adestination group dependent busy-port mask, obtained from a remoteswitch busy global port table can be applied to global minimal pathcandidate ports. Correspondingly, when a frame is being routed in itsdestination group, a destination switch-dependent busy-port mask,obtained from a remote switch busy local port table can be applied tolocal non-minimal path candidate ports. Thus, the use of loadinformation need not be limited to simply determining ports ofintermediate switches. Upon a port being marked as busy in a busy portmask, that port may be removed or taken out of consideration as acandidate port. As illustrated in FIG. 5 , and described above,load-based adaptive selection can narrow surviving candidate ports to aleast loaded candidate port. A path along which the packet is routed canbe selected to include this least loaded port, and the packet isultimately routed through the selected one of the plurality of switchports.

It should be noted that the terms “optimize,” “optimal” and the like asused herein can be used to mean making or achieving performance aseffective or perfect as possible. However, as one of ordinary skill inthe art reading this document will recognize, perfection cannot alwaysbe achieved. Accordingly, these terms can also encompass making orachieving performance as good or effective as possible or practicalunder the given circumstances, or making or achieving performance betterthan that which can be achieved with other settings or parameters.

FIG. 9 depicts a block diagram of an example computer system 900 inwhich various of the embodiments described herein may be implemented.The computer system 900 includes a bus 902 or other communicationmechanism for communicating information, one or more hardware processors904 coupled with bus 902 for processing information.

Hardware processor(s) 904 may be, for example, one or more generalpurpose microprocessors.

The computer system 900 also includes a main memory 906, such as arandom access memory (RAM), cache and/or other dynamic storage devices,coupled to bus 902 for storing information and instructions to beexecuted by processor 904. Main memory 906 also may be used for storingtemporary variables or other intermediate information during executionof instructions to be executed by processor 904. Such instructions, whenstored in storage media accessible to processor 904, render computersystem 900 into a special-purpose machine that is customized to performthe operations specified in the instructions.

The computer system 900 further includes a read only memory (ROM) 908 orother static storage device coupled to bus 902 for storing staticinformation and instructions for processor 904. A storage device 910,such as a magnetic disk, optical disk, or USB thumb drive (Flash drive),etc., is provided and coupled to bus 902 for storing information andinstructions.

The computer system 900 may be coupled via bus 902 to a display 912,such as a liquid crystal display (LCD) (or touch screen), for displayinginformation to a computer user. An input device 914, includingalphanumeric and other keys, is coupled to bus 902 for communicatinginformation and command selections to processor 904. Another type ofuser input device is cursor control 916, such as a mouse, a trackball,or cursor direction keys for communicating direction information andcommand selections to processor 904 and for controlling cursor movementon display 912. In some embodiments, the same direction information andcommand selections as cursor control may be implemented via receivingtouches on a touch screen without a cursor.

The computing system 900 may include a user interface module toimplement a GUI that may be stored in a mass storage device asexecutable software codes that are executed by the computing device(s).This and other modules may include, by way of example, components, suchas software components, object-oriented software components, classcomponents and task components, processes, functions, attributes,procedures, subroutines, segments of program code, drivers, firmware,microcode, circuitry, data, databases, data structures, tables, arrays,and variables.

In general, the word “component,” “engine,” “system,” “database,” datastore,” and the like, as used herein, can refer to logic embodied inhardware or firmware, or to a collection of software instructions,possibly having entry and exit points, written in a programminglanguage, such as, for example, Java, C or C++. A software component maybe compiled and linked into an executable program, installed in adynamic link library, or may be written in an interpreted programminglanguage such as, for example, BASIC, Perl, or Python. It will beappreciated that software components may be callable from othercomponents or from themselves, and/or may be invoked in response todetected events or interrupts. Software components configured forexecution on computing devices may be provided on a computer readablemedium, such as a compact disc, digital video disc, flash drive,magnetic disc, or any other tangible medium, or as a digital download(and may be originally stored in a compressed or installable format thatrequires installation, decompression or decryption prior to execution).Such software code may be stored, partially or fully, on a memory deviceof the executing computing device, for execution by the computingdevice. Software instructions may be embedded in firmware, such as anEPROM. It will be further appreciated that hardware components may becomprised of connected logic units, such as gates and flip-flops, and/ormay be comprised of programmable units, such as programmable gate arraysor processors.

The computer system 900 may implement the techniques described hereinusing customized hard-wired logic, one or more ASICs or FPGAs, firmwareand/or program logic which in combination with the computer systemcauses or programs computer system 900 to be a special-purpose machine.According to one embodiment, the techniques herein are performed bycomputer system 900 in response to processor(s) 904 executing one ormore sequences of one or more instructions contained in main memory 906.Such instructions may be read into main memory 906 from another storagemedium, such as storage device 910. Execution of the sequences ofinstructions contained in main memory 906 causes processor(s) 904 toperform the process steps described herein. In alternative embodiments,hard-wired circuitry may be used in place of or in combination withsoftware instructions.

The term “non-transitory media,” and similar terms, as used hereinrefers to any media that store data and/or instructions that cause amachine to operate in a specific fashion. Such non-transitory media maycomprise non-volatile media and/or volatile media. Non-volatile mediaincludes, for example, optical or magnetic disks, such as storage device910. Volatile media includes dynamic memory, such as main memory 906.Common forms of non-transitory media include, for example, a floppydisk, a flexible disk, hard disk, solid state drive, magnetic tape, orany other magnetic data storage medium, a CD-ROM, any other optical datastorage medium, any physical medium with patterns of holes, a RAM, aPROM, and EPROM, a FLASH-EPROM, NVRAM, any other memory chip orcartridge, and networked versions of the same.

Non-transitory media is distinct from but may be used in conjunctionwith transmission media. Transmission media participates in transferringinformation between non-transitory media. For example, transmissionmedia includes coaxial cables, copper wire and fiber optics, includingthe wires that comprise bus 902. Transmission media can also take theform of acoustic or light waves, such as those generated duringradio-wave and infra-red data communications.

The computer system 900 also includes a communication interface 918coupled to bus 902. Network interface 918 provides a two-way datacommunication coupling to one or more network links that are connectedto one or more local networks. For example, communication interface 918may be an integrated services digital network (ISDN) card, cable modem,satellite modem, or a modem to provide a data communication connectionto a corresponding type of telephone line. As another example, networkinterface 918 may be a local area network (LAN) card to provide a datacommunication connection to a compatible LAN (or WAN component tocommunicated with a WAN). Wireless links may also be implemented. In anysuch implementation, network interface 918 sends and receiveselectrical, electromagnetic or optical signals that carry digital datastreams representing various types of information.

A network link typically provides data communication through one or morenetworks to other data devices. For example, a network link may providea connection through local network to a host computer or to dataequipment operated by an Internet Service Provider (ISP). The ISP inturn provides data communication services through the world wide packetdata communication network now commonly referred to as the “Internet.”Local network and Internet both use electrical, electromagnetic oroptical signals that carry digital data streams. The signals through thevarious networks and the signals on network link and throughcommunication interface 918, which carry the digital data to and fromcomputer system 900, are example forms of transmission media.

The computer system 900 can send messages and receive data, includingprogram code, through the network(s), network link and communicationinterface 918. In the Internet example, a server might transmit arequested code for an application program through the Internet, the ISP,the local network and the communication interface 918.

The received code may be executed by processor 904 as it is received,and/or stored in storage device 910, or other non-volatile storage forlater execution.

Each of the processes, methods, and algorithms described in thepreceding sections may be embodied in, and fully or partially automatedby, code components executed by one or more computer systems or computerprocessors comprising computer hardware. The one or more computersystems or computer processors may also operate to support performanceof the relevant operations in a “cloud computing” environment or as a“software as a service” (SaaS). The processes and algorithms may beimplemented partially or wholly in application-specific circuitry. Thevarious features and processes described above may be used independentlyof one another, or may be combined in various ways. Differentcombinations and sub-combinations are intended to fall within the scopeof this disclosure, and certain method or process blocks may be omittedin some implementations. The methods and processes described herein arealso not limited to any particular sequence, and the blocks or statesrelating thereto can be performed in other sequences that areappropriate, or may be performed in parallel, or in some other manner.Blocks or states may be added to or removed from the disclosed exampleembodiments. The performance of certain of the operations or processesmay be distributed among computer systems or computers processors, notonly residing within a single machine, but deployed across a number ofmachines.

As used herein, a circuit might be implemented utilizing any form ofhardware, software, or a combination thereof. For example, one or moreprocessors, controllers, ASICs, PLAs, PALs, CPLDs, FPGAs, logicalcomponents, software routines or other mechanisms might be implementedto make up a circuit. In implementation, the various circuits describedherein might be implemented as discrete circuits or the functions andfeatures described can be shared in part or in total among one or morecircuits. Even though various features or elements of functionality maybe individually described or claimed as separate circuits, thesefeatures and functionality can be shared among one or more commoncircuits, and such description shall not require or imply that separatecircuits are required to implement such features or functionality. Wherea circuit is implemented in whole or in part using software, suchsoftware can be implemented to operate with a computing or processingsystem capable of carrying out the functionality described with respectthereto, such as computer system 900.

As used herein, the term “or” may be construed in either an inclusive orexclusive sense. Moreover, the description of resources, operations, orstructures in the singular shall not be read to exclude the plural.Conditional language, such as, among others, “can,” “could,” “might,” or“may,” unless specifically stated otherwise, or otherwise understoodwithin the context as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements and/or steps.

Terms and phrases used in this document, and variations thereof, unlessotherwise expressly stated, should be construed as open ended as opposedto limiting. Adjectives such as “conventional,” “traditional,” “normal,”“standard,” “known,” and terms of similar meaning should not beconstrued as limiting the item described to a given time period or to anitem available as of a given time, but instead should be read toencompass conventional, traditional, normal, or standard technologiesthat may be available or known now or at any time in the future. Thepresence of broadening words and phrases such as “one or more,” “atleast,” “but not limited to” or other like phrases in some instancesshall not be read to mean that the narrower case is intended or requiredin instances where such broadening phrases may be absent.

What is claimed is:
 1. A method of passing data amongst a plurality ofswitches having a plurality of links attached between the plurality ofswitches, the method comprising: at a switch, receiving a plurality ofload signals from a plurality of neighboring switches, each of theplurality of load signals comprising a set of values indicative of aload at each of the plurality of neighboring switches providing the loadsignal, each value within the set of values providing an indication foreach link of the plurality of links attached thereto as to whether thelink is busy or quiet; and based upon the plurality of load signals,selecting an output link for routing a received packet and routing thereceived packet via the selected output link.
 2. The method of claim 1,wherein the switch comprises a source switch.
 3. The method of claim 1,wherein the indication as to whether the link is busy comprises a remoteswitch busy port mask characterizing ports of the neighboring switches,one or more of the remote switch busy port masks being transformed toform entries of a remote switch busy global port table and one or moreof the remote switch busy port masks being transformed to form entriesof a remote switch busy local port table, the remote switch busy portmasks being received from the neighboring switches.
 4. The method ofclaim 3, wherein the remote switch busy global port table is indexed inaccordance with destination group identifiers corresponding to those ofthe destination groups of the received packets.
 5. The method of claim4, wherein a fabric routing function instance of the switch, inaccordance with an executed routing algorithm, determines a recommendedport to which the received packet is to be routed subsequent tofiltering out candidate ports based on a determination that the filteredout candidate ports are busy in accordance with the indexed entry in theremote switch busy global port table.
 6. The method of claim 3, whereinthe remote switch busy local port table is indexed in accordance withswitch identifiers corresponding to those of the destination switches ofthe received packets.
 7. The method of claim 6, wherein a fabric routingfunction instance of the switch, in accordance with an executed routingalgorithm, determines a recommended port to which the received packet isto be routed subsequent to filtering out candidate ports based on adetermination that the filtered out candidate ports are busy inaccordance with the indexed entry in the remote switch busy local porttable.
 8. A switch, comprising: an application-specific integratedcircuit (ASIC) to: receive a plurality of load signals from a pluralityof neighboring switches, each of the plurality of load signalscomprising a set of values indicative of a load at each of the pluralityof neighboring switches providing the load signal, each value within theset of values providing an indication for each link of the plurality oflinks attached thereto as to whether the link is busy or quiet; basedupon the received plurality of load signals, select an output link forrouting a received packet; and route the packet via the selected outputlink.
 9. The switch of claim 8, wherein the indication as to whether thelink is busy comprises a remote switch busy port mask characterizingports of the neighboring switches, one or more of the remote switch busyport masks being transformed to form entries of a remote switch busyglobal port table and one or more of the remote switch busy port masksbeing transformed to form entries of a remote switch busy local porttable, the remote switch busy port masks being received from theneighboring switches.
 10. The switch of claim 9, wherein the remoteswitch busy global port table is indexed in accordance with destinationgroup identifiers corresponding to those of the destination groups ofthe received packets.
 11. The switch of claim 10, wherein the ASICcomprises a fabric routing function instance which, in accordance withan executed routing algorithm, determines a recommended port to whichthe received packet is to be routed subsequent to filtering outcandidate ports based on a determination that the filtered out candidateports are busy in accordance with the indexed entry in the remote switchbusy global port table
 12. The switch of claim 9, wherein the remoteswitch busy local port table is indexed in accordance with switchidentifiers corresponding to those of the destination switches of thereceived packets.
 13. The switch of claim 12, wherein the ASIC comprisesa fabric routing function instance which, in accordance with an executedrouting algorithm, determines a recommended port to which the receivedpacket is to be routed subsequent to filtering out candidate ports basedon a determination that the filtered out candidate ports are busy inaccordance with the indexed entry in the remote switch busy local porttable.
 14. A system, comprising: a plurality of switches interconnectedto form a switch fabric; wherein a first switch of the plurality ofswitches receives a load signal from neighboring switches of theplurality of switches, each of the plurality of load signals comprisinga set of values indicative of a load at each of the plurality ofneighboring switches providing the load signal, each value within theset of values providing an indication for each link of the plurality oflinks attached thereto as to whether the link is busy or quiet; andwherein based upon the plurality of load signals, the first switchselects an output link for routing a received packet and routing thereceived packet via the selected output link.
 15. The system of claim14, wherein the indication as to whether the link is busy comprises aremote switch busy port mask characterizing ports of the neighboringswitches, one or more of the remote switch busy port masks beingtransformed to form entries of a remote switch busy global port tableand one or more of the remote switch busy port masks being transformedto form entries of a remote switch busy local port table, the remoteswitch busy port masks being received from the neighboring switches. 16.The system of claim 15, wherein the remote switch busy global port tableis indexed in accordance with destination group identifierscorresponding to those of the destination groups of the receivedpackets.
 17. The system of claim 16, wherein subsets of the neighboringswitches comprise global minimal paths to reach the destination groups.18. The system of claim 16, wherein a fabric routing function instanceof the first switch, in accordance with an executed routing algorithm,determines a recommended port to which the received packet is to berouted subsequent to filtering out candidate ports based on adetermination that the filtered out candidate ports are busy inaccordance with the indexed entry in the remote switch busy global porttable.
 19. The system of claim 15, wherein the remote switch busy localport table is indexed in accordance with switch identifierscorresponding to those of the destination switches of the receivedpackets.
 20. The system of claim 19, wherein subsets of the neighboringswitches comprise local non-minimal and local minimal paths to thedestination switches.
 21. The system of claim 19, wherein a fabricrouting function instance of the first switch, in accordance with anexecuted routing algorithm, determines a recommended port to which thereceived packet is to be routed subsequent to filtering out candidateports based on a determination that the filtered out candidate ports arebusy in accordance with the indexed entry in the remote switch busylocal port table.